Blur App Preview in iOS Apps

Last updated June 3, 2025 by Appdome

This Knowledge Base article describes how to use Appdome’s AI in your CI/CD pipeline to continuously deliver plugins that Blur App Preview in iOS apps.

What is the "Blur App Preview" protection?

Blur App Preview is a mobile privacy protection that prevents sensitive app data from being exposed in OS-level screenshots, screen recordings, or the app switcher when a user minimizes the app. Attackers can exploit cached screen images or preview snapshots of mobile apps to access confidential user data—such as account balances, medical details, or session states—outside the app’s secure environment. This threat is particularly concerning for finance, healthcare, and enterprise apps, where background app data may persist and be harvested without user awareness. Implementing blur protections is essential for data loss prevention (DLP), especially in regulated environments such as HIPAA or PCI DSS, where unintentional data leakage can violate compliance. Since operating systems do not offer built-in tools for secure preview handling, developers often struggle to prevent this exposure natively, making a seamless defense solution critical for continuous mobile privacy.

How Appdome Protects iOS Apps Using "Blur App Preview"

Appdome’s dynamic Blur App Preview plugin for iOS automatically blurs the app’s preview image when it is minimized or sent to the background. This prevents sensitive data from appearing in the app switcher or being cached by the OS. Developers can implement this protection without code, SDKs, or external servers. The protection is enforced at runtime, ensuring continuous privacy coverage.

Prerequisites for Using Appdome's Blur App Preview Plugins:

To use Appdome’s mobile app security build system to Blur App Preview , you’ll need:

Appdome account (create a free Appdome account here)
A license for Blur App Preview
Mobile App (.ipa for iOS)
Signing Credentials (see Signing Secure Android apps and Signing Secure iOS apps)

How to Implement Blur App Preview in iOS Apps Using Appdome

On Appdome, follow these 3 simple steps to create self-defending iOS Apps that Blur App Preview without an SDK or gateway:

Designate the Mobile App to be protected.
1. Upload an app via the Appdome Mobile Defense platform GUI or via Appdome’s DEV-API or CI/CD Plugins.
2. iOS Formats: .ipa
3. Blur App Preview is compatible with: Obj-C, Java, Swift, Flutter, React Native, Unity, Xamarin, Cordova and other iOS apps.
Select the defense: Blur App Preview.

Create and name the Fusion Set (security template) that will contain the Blur App Preview feature as shown below:

Figure 1: Fusion Set that will contain the Blur App Preview feature

Follow the steps in Sections 2.2-2.2.2 of this article to add the Blur App Preview feature to your Fusion Set via the Appdome Console.

When you select the Blur App Preview you'll notice that the Fusion Set you created in step 2.1 now bears the icon of the protection category that contains Blur App Preview.

Figure 2: Fusion Set that displays the newly added Blur App Preview protection
Note: Annotating the Fusion Set to identify the protection(s) selected is optional only (not mandatory).

Open the Fusion Set Detail Summary by clicking the “...” symbol on the far-right corner of the Fusion Set. Copy the Fusion Set ID from the Fusion Set Detail Summary (as shown below):

Figure 3: Fusion Set Detail Summary

Follow the instructions below to use the Fusion Set ID inside any standard mobile DevOps or CI/CD toolkit like Bitrise, Jenkins, Travis, Team City, Circle CI or other system:

Refer to the Appdome API Reference Guide for API building instructions.

Look for sample APIs in Appdome’s GitHub Repository.

Add the Blur App Preview feature to your security template.

Navigate to Build > Anti ATO tab > Mobile Account Protection section in the Appdome Console.
Like all other options in ONEShield™, Blur App Preview is turned on by default, as shown below:
Figure 4: Selecting Blur App Preview
Note: The App Compromise Notification contains an easy to follow default remediation path for the mobile app end user. You can customize this message as required to achieve brand specific support, workflow or other messaging.

Toggle On > Blur App Preview.

Figure 4: Selecting Blur App Preview
Note: The Appdome Platform displays the Mobile Operation Systems supported by each defense in real-time. For more details, see our OS Support Policy KB.

Configure the User Experience Options for Blur App Preview:
With Threat-Events™ OFF, Appdome provides several user experience options for mobile brands and developers.

App Compromise Notification: Customize the pop-up or toast Appdome uses to notify the user when a threat is present while using the protected mobile app.

Short message Option. This is available for mobile devices that allow a banner notification for security events.

Localized Message Option. Allows Appdome users to support global languages in security notifications.

Figure 5: Default User Experience Options for Appdome’s App Preview

Blur App Preview Threat Code™. Appdome uses AI to generate a unique code each time Blur App Preview is triggered by an active threat on the mobile device. Use the code in Appdome Threat Resolution Center™ to help end users identify, find and resolve active threats on the personal mobile devices.

Initiate the build command either by clicking Build My App at the bottom of the Build Workflow (shown in Figure 4) or via your CI/CD as described in Section 2.1.4.

Congratulations! The Blur App Preview protection is now added to the mobile app

Certify the Blur App Preview feature in iOS Apps

After building Blur App Preview, Appdome generates a Certified Secure™ certificate to guarantee that the Blur App Preview protection has been added and is protecting the app. To verify that the Blur App Preview protection has been added to the mobile app, locate the protection in the Certified Secure™ certificate as shown below:

Figure 6: Certified Secure™ certificate

Each Certified Secure™ certificate provides DevOps and DevSecOps organizations the entire workflow summary, audit trail of each build, and proof of protection that Blur App Preview has been added to each iOS app. Certified Secure provides instant and in-line DevSecOps compliance certification that Blur App Preview and other mobile app security features are in each build of the mobile app.

Using Threat-Events™ for App Preview Intelligence and Control in iOS Apps

Appdome Threat-Events™ provides consumable in-app mobile app attack intelligence and defense control when App Preview is detected. To consume and use Threat-Events™ for App Preview in iOS Apps, use AddObserverForName in Notification Center, and the code samples for Threat-Events™ for App Preview shown below.

The specifications and options for Threat-Events™ for App Preview are:

Threat-Event™ Elements Blur App Preview Method Detail

Appdome Feature Name Blur App Preview

Threat-Event Mode

OFF, IN-APP DEFENSE Appdome detects, defends and notifies user (standard OS dialog) using customizable messaging.

ON, IN-APP DETECTION Appdome detects the attack or threat and passes the event in a standard format to the app for processing (app chooses how and when to enforce).

ON, IN-APP DEFENSE Uses Appdome Enforce mode for any attack or threat and passes the event in a standard format to the app for processing (gather intel on attacks and threats without losing any protection).

Certified Secure™ Threat Event Check

Visible in ThreatScope™

Developer Parameters for Bluring App Preview Threat-Event™

Threat-Event NAME BlockedScreenCaptureEvent

Threat-Event DATA reasonData

Threat-Event CODE reasonCode

Threat-Event REF 2560

Threat-Event SCORE
currentThreatEventScore Current Threat-Event score

threatEventsScore Total Threat-events score

Threat-Event Context Keys

Timestamp The exact time the threat event was triggered, recorded in milliseconds since epoch

message Message displayed for the user on event

externalID The external ID of the event which can be listened via Threat Events

osVersion OS version of the current device

deviceModel Current device model

deviceManufacturer The manufacturer of the current device

fusedAppToken The task ID of the Appdome fusion of the currently running app

kernelInfo Info about the kernel: system name, node name, release, version and machine.

deviceID Current device ID

reasonCode Reason code of the occurred event

threatCode The last six characters of the threat code specify the OS, allowing the Threat Resolution Center to address the attack on the affected device.

context Context of the security event

With Threat-Events™ enabled (turned ON), iOS developers can get detailed attack intelligence and granular defense control in iOS applications and create amazing user experiences for all mobile end users when App Preview is detected.

The following is a code sample for native iOS apps, which uses all values in the specification above for Blur App Preview:

Important! Replace all placeholder instances of <Context Key> with the specific name of your threat event context key across all language examples. This is crucial to ensure your code functions correctly with the intended event data. For example, The <Context Key> could be the message, externalID, OS Version, reason code, etc.

let center = NotificationCenter.default center.addObserver(forName: Notification.Name("BlockedScreenCaptureEvent"), object: nil, queue: nil) { (note) in guard let usrInf = note.userInfo else { return } let message = usrInf["message"]; // Message shown to the user let reasonData = usrInf["reasonData"]; // Threat detection cause let reasonCode = usrInf["reasonCode"]; // Event reason code // Current threat event score let currentThreatEventScore = usrInf["currentThreatEventScore"]; // Total threat events score let threatEventsScore = usrInf["threatEventsScore"]; // Replace '' with your specific event context key // let variable = usrInf[""]; // Your logic goes here (Send data to Splunk/Dynatrace/Show Popup...) }

x
1
21
1
21
1
21
1
21

1
let center = NotificationCenter.default
2
center.addObserver(forName: Notification.Name("BlockedScreenCaptureEvent"), object: nil, queue: nil) { (note) in
3
guard let usrInf = note.userInfo else {
4
return
5
}
6

7
let message = usrInf["message"]; // Message shown to the user
8
let reasonData = usrInf["reasonData"]; // Threat detection cause
9
let reasonCode = usrInf["reasonCode"]; // Event reason code
10

11
// Current threat event score
12
let currentThreatEventScore = usrInf["currentThreatEventScore"];
13

14
// Total threat events score
15
let threatEventsScore = usrInf["threatEventsScore"];
16

17
// Replace '<Context Key>' with your specific event context key
18
// let variable = usrInf["<Context Key>"];
19

20
// Your logic goes here (Send data to Splunk/Dynatrace/Show Popup...)
21
}

[[NSNotificationCenter defaultCenter] addObserverForName: @"BlockedScreenCaptureEvent" object:nil queue:nil usingBlock:^(NSNotification *org_note) { __block NSNotification *note = org_note; dispatch_async(dispatch_get_main_queue(), ^(void) { // Message shown to the user NSString *message = [[note userInfo] objectForKey:@"message"]; // Threat detection cause NSString *reasonData = [[note userInfo] objectForKey:@"reasonData"]; // Event reason code NSString *reasonCode = [[note userInfo] objectForKey:@"reasonCode"]; // Current threat event score NSString *currentThreatEventScore = [[note userInfo] objectForKey:@"currentThreatEventScore"]; // Total threat events score NSString *threatEventsScore = [[note userInfo] objectForKey:@"threatEventsScore"]; // Replace '' with your specific event context key // NSString *variable = [[note userInfo] objectForKey:@""]; // Your logic goes here (Send data to Splunk/Dynatrace/Show Popup...) }); }];

xxxxxxxxxx
1
20
1
15
1
15
1
15

1
[[NSNotificationCenter defaultCenter] addObserverForName: @"BlockedScreenCaptureEvent" object:nil queue:nil usingBlock:^(NSNotification *org_note) {
2
__block NSNotification *note = org_note;
3
dispatch_async(dispatch_get_main_queue(), ^(void) {
4

5
// Message shown to the user
6
NSString *message = [[note userInfo] objectForKey:@"message"];
7

8
// Threat detection cause
9
NSString *reasonData = [[note userInfo] objectForKey:@"reasonData"];
10

11
// Event reason code
12
NSString *reasonCode = [[note userInfo] objectForKey:@"reasonCode"];
13

14
// Current threat event score
15
NSString *currentThreatEventScore = [[note userInfo] objectForKey:@"currentThreatEventScore"];
16

17
// Total threat events score
18
NSString *threatEventsScore = [[note userInfo] objectForKey:@"threatEventsScore"];
19

20
// Replace '<Context Key>' with your specific event context key
21
// NSString *variable = [[note userInfo] objectForKey:@"<Context Key>"];
22

23
// Your logic goes here (Send data to Splunk/Dynatrace/Show Popup...)
24
});
25
}];

const { ADDevEvents } = NativeModules; const aDDevEvents = new NativeEventEmitter(ADDevEvents); function registerToDevEvent(action, callback) { NativeModules.ADDevEvents.registerForDevEvent(action); aDDevEvents.addListener(action, callback); } export function registerToAllEvents() { registerToDevEvent( "BlockedScreenCaptureEvent", (userinfo) => Alert.alert(JSON.stringify(userinfo)) var message = userinfo["message"] // Message shown to the user var reasonData = userinfo["reasonData"] // Threat detection cause var reasonCode = userinfo["reasonCode"] // Event reason code // Current threat event score var currentThreatEventScore = userinfo["currentThreatEventScore"] // Total threat events score var threatEventsScore = userinfo["threatEventsScore"] // Replace '' with your specific event context key // var variable = userinfo[""] // Your logic goes here (Send data to Splunk/Dynatrace/Show Popup...) ); }

xxxxxxxxxx
1
20
1
15
1
15
1
15
2
29

1
const { ADDevEvents } = NativeModules;
2
const aDDevEvents = new NativeEventEmitter(ADDevEvents);
3

4
function registerToDevEvent(action, callback) {
5
NativeModules.ADDevEvents.registerForDevEvent(action);
6
aDDevEvents.addListener(action, callback);
7
}
8

9
export function registerToAllEvents() {
10
registerToDevEvent(
11
"BlockedScreenCaptureEvent",
12
(userinfo) => Alert.alert(JSON.stringify(userinfo))
13

14
var message = userinfo["message"] // Message shown to the user
15
var reasonData = userinfo["reasonData"] // Threat detection cause
16
var reasonCode = userinfo["reasonCode"] // Event reason code
17

18
// Current threat event score
19
var currentThreatEventScore = userinfo["currentThreatEventScore"]
20

21
// Total threat events score
22
var threatEventsScore = userinfo["threatEventsScore"]
23

24
// Replace '<Context Key>' with your specific event context key
25
// var variable = userinfo["<Context Key>"]
26

27
// Your logic goes here (Send data to Splunk/Dynatrace/Show Popup...)
28
);
29
}

RegisterReceiver(new ThreatEventReceiver(), new IntentFilter("BlockedScreenCaptureEvent")); class ThreatEventReceiver : BroadcastReceiver { public override void OnReceive(Context context, Intent intent) { String message = intent.GetStringExtra("message"); // Message shown to the user String reasonData = intent.GetStringExtra("reasonData"); // Threat detection cause String reasonCode = intent.GetStringExtra("reasonCode"); // Event reason code // Current threat event score String currentThreatEventScore = intent.GetStringExtra("currentThreatEventScore"); // Total threat events score String threatEventsScore = intent.GetStringExtra("threatEventsScore"); // Replace '' with your specific event context key // String variable = intent.GetStringExtra(""); // Your logic goes here (Send data to Splunk/Dynatrace/Show Popup...) } }

x
27

1
RegisterReceiver(new ThreatEventReceiver(), new IntentFilter("BlockedScreenCaptureEvent"));
2

3
class ThreatEventReceiver : BroadcastReceiver
4
{
5
public override void OnReceive(Context context, Intent intent)
6
{
7
// Message shown to the user
8
String message = intent.GetStringExtra("message");
9

10
// Threat detection cause
11
String reasonData = intent.GetStringExtra("reasonData");
12

13
// Event reason code
14
String reasonCode = intent.GetStringExtra("reasonCode");
15

16
// Current threat event score
17
String currentThreatEventScore = intent.GetStringExtra("currentThreatEventScore");
18

19
// Total threat events score
20
String threatEventsScore = intent.GetStringExtra("threatEventsScore");
21

22
// Replace '<Context Key>' with your specific event context key
23
// String variable = intent.GetStringExtra("<Context Key>");
24

25
// Your logic goes here (Send data to Splunk/Dynatrace/Show Popup...)
26
}
27
}

NSNotificationCenter.DefaultCenter.AddObserver( (NSString)"BlockedScreenCaptureEvent", // Threat-Event Identifier delegate (NSNotification notification) { // Message shown to the user var message = notification.UserInfo.ObjectForKey("message"); // Threat detection cause var reasonData = notification.UserInfo.ObjectForKey("reasonData"); // Event reason code var reasonCode = notification.UserInfo.ObjectForKey("reasonCode"); // Current threat event score var currentThreatEventScore = notification.UserInfo.ObjectForKey("currentThreatEventScore"); // Total threat events score var threatEventsScore = notification.UserInfo.ObjectForKey("threatEventsScore"); // Replace '' with your specific event context key // var variable = notification.UserInfo.ObjectForKey(""); // Your logic goes here (Send data to Splunk/Dynatrace/Show Popup...) } );

x

1
NSNotificationCenter.DefaultCenter.AddObserver(
2
(NSString)"BlockedScreenCaptureEvent", // Threat-Event Identifier
3
delegate (NSNotification notification)
4
{
5
// Message shown to the user
6
var message = notification.UserInfo.ObjectForKey("message");
7

8
// Threat detection cause
9
var reasonData = notification.UserInfo.ObjectForKey("reasonData");
10

11
// Event reason code
12
var reasonCode = notification.UserInfo.ObjectForKey("reasonCode");
13

14
// Current threat event score
15
var currentThreatEventScore = notification.UserInfo.ObjectForKey("currentThreatEventScore");
16

17
// Total threat events score
18
var threatEventsScore = notification.UserInfo.ObjectForKey("threatEventsScore");
19

20
// Replace '<Context Key>' with your specific event context key
21
// var variable = notification.UserInfo.ObjectForKey("<Context Keys>");
22

23
// Your logic goes here (Send data to Splunk/Dynatrace/Show Popup...)
24
}
25
);

window.broadcaster.addEventListener("BlockedScreenCaptureEvent", function(userInfo) { var message = userInfo.message // Message shown to the user var reasonData = userInfo.reasonData // Threat detection cause var reasonCode = userInfo.reasonCode // Event reason code // Current threat event score var currentThreatEventScore = userInfo.currentThreatEventScore // Total threat events score var threatEventsScore = userInfo.threatEventsScore // Replace '' with your specific event context key // var variable = userInfo. // Your logic goes here (Send data to Splunk/Dynatrace/Show Popup...) });

xxxxxxxxxx
1
20
1
15
1
15
1
15
2
29

1
window.broadcaster.addEventListener("BlockedScreenCaptureEvent", function(userInfo) {
2
var message = userInfo.message // Message shown to the user
3
var reasonData = userInfo.reasonData // Threat detection cause
4
var reasonCode = userInfo.reasonCode // Event reason code
5

6
// Current threat event score
7
var currentThreatEventScore = userInfo.currentThreatEventScore
8

9
// Total threat events score
10
var threatEventsScore = userInfo.threatEventsScore
11

12
// Replace '<Context Key>' with your specific event context key
13
// var variable = userInfo.<Context Keys>
14

15
// Your logic goes here (Send data to Splunk/Dynatrace/Show Popup...)
16
});

import 'dart:async'; import 'package:flutter/material.dart'; import 'package:flutter/services.dart'; class PlatformChannel extends StatefulWidget { const PlatformChannel({super.key}); @override State createState() => _PlatformChannelState(); } class _PlatformChannelState extends State { // Replace with your EventChannel name static const String _eventChannelName = "BlockedScreenCaptureEvent"; static const EventChannel _eventChannel = EventChannel(_eventChannelName); @override void initState() { super.initState(); _eventChannel.receiveBroadcastStream().listen(_onEvent, onError: _onError); } void _onEvent(Object? event) { setState(() { // Adapt this section based on your specific event data structure var eventData = event as Map; // Example: Accessing 'externalID' field from the event var externalID = eventData['externalID']; // Customize the rest of the fields based on your event structure String message = eventData['message']; // Message shown to the user String reasonData = eventData['reasonData']; // Threat detection cause String reasonCode = eventData['reasonCode']; // Event reason code // Current threat event score String currentThreatEventScore = eventData['currentThreatEventScore']; // Total threat events score String threatEventsScore = eventData['threatEventsScore']; // Replace '' with your specific event context key // String variable = eventData['']; }); } // Your logic goes here (Send data to Splunk/Dynatrace/Show Popup...) }

x

1
import 'dart:async';
2
import 'package:flutter/material.dart';
3
import 'package:flutter/services.dart';
4

5
class PlatformChannel extends StatefulWidget {
6
const PlatformChannel({super.key});
7

8
@override
9
State<PlatformChannel> createState() => _PlatformChannelState();
10
}
11

12
class _PlatformChannelState extends State<PlatformChannel> {
13
// Replace with your EventChannel name
14
static const String _eventChannelName = "BlockedScreenCaptureEvent";
15
static const EventChannel _eventChannel = EventChannel(_eventChannelName);
16

17
@override
18
void initState() {
19
super.initState();
20
_eventChannel.receiveBroadcastStream().listen(_onEvent, onError: _onError);
21
}
22

23
void _onEvent(Object? event) {
24
setState(() {
25
// Adapt this section based on your specific event data structure
26
var eventData = event as Map;
27

28
// Example: Accessing 'externalID' field from the event
29
var externalID = eventData['externalID'];
30

31
// Customize the rest of the fields based on your event structure
32
String message = eventData['message']; // Message shown to the user
33
String reasonData = eventData['reasonData']; // Threat detection cause
34
String reasonCode = eventData['reasonCode']; // Event reason code
35

36
// Current threat event score
37
String currentThreatEventScore = eventData['currentThreatEventScore'];
38

39
// Total threat events score
40
String threatEventsScore = eventData['threatEventsScore'];
41

42
// Replace '<Context Key>' with your specific event context key
43
// String variable = eventData['<Context Keys>'];
44
});
45
}
46

47
// Your logic goes here (Send data to Splunk/Dynatrace/Show Popup...)
48
}

Using Appdome, there are no development or coding prerequisites to build secured iOS Apps by using Blur App Preview. There is no SDK and no library to code or implement in the app and no gateway to deploy in your network. All protections are built into each app and the resulting app is self-defending and self-protecting.

Releasing and Publishing Mobile Apps with Blur App Preview

After successfully securing your app by using Appdome, there are several available options to complete your project, depending on your app lifecycle or workflow. These include:

Customizing, Configuring & Branding Secure Mobile Apps.

Deploying/Publishing Secure mobile apps to Public or Private app stores.

Releasing Secured Android & iOS Apps built on Appdome.

Related Articles:

How to Protect Floating Windows and Dynamic Content in Android Apps

How to Protect Android & iOS Apps from Screen Sharing Malware

Mobile User Experience Options When Copy/Paste is Not Allowed for DLP

How Do I Learn More?

If you have any questions, please send them our way at support.appdome.com or via the chat window on the Appdome platform.

Thank you!

Thanks for visiting Appdome! Our mission is to secure every app on the planet by making mobile app security easy. We hope we’re living up to the mission with your project.

Blur App Preview in iOS Apps

What is the "Blur App Preview" protection?

How Appdome Protects iOS Apps Using "Blur App Preview"

Prerequisites for Using Appdome's Blur App Preview Plugins:

How to Implement Blur App Preview in iOS Apps Using Appdome

Designate the Mobile App to be protected.

Upload an app via the Appdome Mobile Defense platform GUI or via Appdome’s DEV-API or CI/CD Plugins.

Select the defense: Blur App Preview.

Add the Blur App Preview feature to your security template.

Certify the Blur App Preview feature in iOS Apps

Using Threat-Events™ for App Preview Intelligence and Control in iOS Apps

Related Articles:

How Do I Learn More?

Thank you!

Device Binding in the Age of AI

How Persistent Mobile Identity Delivers Stronger API Protection

How App & Install Binding Stop Social Engineering in Mobile Apps

Eliminating Mobile Ad Fraud with IDAnchor™

Threat-Event™ Elements	Blur App Preview Method Detail
Appdome Feature Name	Blur App Preview
Threat-Event Mode
OFF, IN-APP DEFENSE	Appdome detects, defends and notifies user (standard OS dialog) using customizable messaging.
ON, IN-APP DETECTION	Appdome detects the attack or threat and passes the event in a standard format to the app for processing (app chooses how and when to enforce).
ON, IN-APP DEFENSE	Uses Appdome Enforce mode for any attack or threat and passes the event in a standard format to the app for processing (gather intel on attacks and threats without losing any protection).
Certified Secure™ Threat Event Check
Visible in ThreatScope™
Developer Parameters for Bluring App Preview Threat-Event™
Threat-Event NAME	BlockedScreenCaptureEvent
Threat-Event DATA	reasonData
Threat-Event CODE	reasonCode
Threat-Event REF	2560
Threat-Event SCORE
currentThreatEventScore	Current Threat-Event score
threatEventsScore	Total Threat-events score

Threat-Event Context Keys
Timestamp	The exact time the threat event was triggered, recorded in milliseconds since epoch
message	Message displayed for the user on event
externalID	The external ID of the event which can be listened via Threat Events
osVersion	OS version of the current device
deviceModel	Current device model
deviceManufacturer	The manufacturer of the current device
fusedAppToken	The task ID of the Appdome fusion of the currently running app
kernelInfo	Info about the kernel: system name, node name, release, version and machine.
deviceID	Current device ID
reasonCode	Reason code of the occurred event
threatCode	The last six characters of the threat code specify the OS, allowing the Threat Resolution Center to address the attack on the affected device.
context	Context of the security event