How to Detect Unknown Sources, Protect Android Apps

Last updated December 6, 2023 by Appdome

This Knowledge Base article describes how to use Appdome’s AI/ML in your CI/CD pipeline to continuously deliver plugins that Detect Unknown Sources in Android apps.

What is Unknown Sources?

With Appdome’s “Detect Unknown Sources” feature integrated into a mobile app, the app protects itself by detecting that the Android OS feature “allow app installs from unknown sources” setting is turned ON and preventing abuse of Unknown Sources to deliver Malware.

Why Detect Unknown Sources in Android Apps?

Unknown Sources is an Android accessibility setting that allows the phone to trust and install applications from any developers, publisher or source outside of the Google Play store. Having this Android OS feature enabled can be used to trick unsuspecting users to install malware disguised as legitimate software.

Prerequisites for Using Appdome's Detect Unknown Sources Plugins:

To use Appdome’s mobile app security build system to Detect Unknown Sources , you’ll need:

How to Implement Detect Unknown Sources in Android Apps Using Appdome

On Appdome, follow these 3 simple steps to create self-defending Android Apps that Detect Unknown Sources without an SDK or gateway:

  1. 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. Android Formats: .apk or .aab
    3. Detect Unknown Sources is compatible with: Java, JS, C++, C#, Kotlin, Flutter, React Native, Unity, Xamarin, Cordova and other Android apps.
  2. Select the defense: Detect Unknown Sources.

      1. Create and name the Fusion Set (security template) that will contain the Detect Unknown Sources feature as shown below:
        fusion set that contains Detect Unknown Sources

        Figure 1: Fusion Set that will contain the Detect Unknown Sources feature

      2. Follow the steps in Sections 2.2-2.2.2 of this article to add the Detect Unknown Sources feature to your Fusion Set via the Appdome Console.

      3. When you select the Detect Unknown Sources you'll notice that the Fusion Set you created in step 2.1 now bears the icon of the protection category that contains Detect Unknown Sources.

        Fusion Set applied Detect Unknown Sources

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

      4. 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): fusion Set Detail Summary image

        Figure 3: Fusion Set Detail Summary

      5. 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:
        1. Refer to the Appdome API Reference Guide for API building instructions.
        2. Look for sample APIs in Appdome’s GitHub Repository.
    1. Add the Detect Unknown Sources feature to your security template.

      1. Navigate to Build > Security tab > OS Integrity section in the Appdome Console.
      2. Toggle On > Detect Unknown Sources.

        (a) Choose to monitor this attack vector by checking the Threat Events checkbox associated with Detect Unknown Sources as shown below.

        (b) To receive mobile Threat Monitoring, check the ThreatScope™ box as shown below. For more details, see our knowledge base article on ThreatScope™ Mobile XDR.
        Detect Unknown Sources option

        Figure 4: Selecting Detect Unknown Sources

        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.

      3. Select the Threat-Event™ in-app mobile Threat Defense and Intelligence policy for Detect Unknown Sources:
        1. Threat-Events™ OFF > In-App Defense

          If the Threat-Events™ setting is not selected. Appdome will detect and defend the user and app by enforcing Unknown Sources.

        2. Threat-Events™ ON > In-App Detection

          When this setting is used, Appdome detects when "allow app install from unknown sources" native OS setting is enabled on the device and passes Appdome’s Threat-Event™ attack intelligence to the app’s business logic for processing, enforcement, and user notification. For more information on consuming and using Appdome Threat-Events™ in the app, see section Using Threat-Events™ to Detect Unknown SourcesDetect Intelligence and Control in Mobile Apps.

        3. Threat-Events™ ON > In-App Defense

          When this setting is used, Appdome detects and defends against Unknown Sources (same as Appdome Enforce) and passes Appdome’s Threat-Event™ attack intelligence to the app’s business logic for processing. For more information on consuming and using Appdome Threat-Events™ in the app, see section Using Threat-Events™ for Detect Unknown SourcesDetect Intelligence and Control in Mobile Apps.

      4. Configure the User Experience Options for Detect Unknown Sources:
        With Threat-Events™ OFF, Appdome provides several user experience options for mobile brands and developers.
        1. 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.
        2. Short message Option. This is available for mobile devices that allow a banner notification for security events.
        3. Localized Message Option. Allows Appdome users to support global languages in security notifications.

          Localized Message

          Figure 5: Default User Experience Options for Appdome’s Unknown Sources

        4. Detect Unknown Sources Threat Code™. Appdome uses AI/ML to generate a unique code each time Detect Unknown Sources 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.
    2. 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 Detect Unknown Sources protection is now added to the mobile app
  3. Certify the Detect Unknown Sources feature in Android Apps

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

    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 Detect Unknown Sources has been added to each Android app. Certified Secure provides instant and in-line DevSecOps compliance certification that Detect Unknown Sources and other mobile app security features are in each build of the mobile app.

Using Threat-Events™ for Unknown Sources Intelligence and Control in Android Apps

Appdome Threat-Events™ provides consumable in-app mobile app attack intelligence and defense control when Unknown Sources is detected. To consume and use Threat-Events™ for Unknown Sources in Android Apps, use registerReceiver in the Application OnCreate, and the code samples for Threat-Events™ for Unknown Sources shown below.

The specifications and options for Threat-Events™ for Unknown Sources are:

Threat-Event™ Elements Detect Unknown Sources Method Detail
Appdome Feature Name Detect Unknown Sources
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 Detecting Unknown Sources Threat-Event™
Threat-Event NAME UnknownSourcesEnabled
Threat-Event DATA reasonData
Threat-Event CODE reasonCode
Threat-Event REF 6701
Threat-Event SCORE
currentThreatEventScore Current Threat-Event score
threatEventsScore Total Threat-events score
Threat-Event Context Keys
message Message displayed for the user on event
failSafeEnforce Timed enforcement against the identified threat
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.
carrierPlmn PLMN of the device. Only available for Android devices.
deviceID Current device ID
reasonCode Reason code of the occurred event
buildDate Appdome fusion date of the current application
devicePlatform OS name of the current device
carrierName Carrier name of the current device. Only available for Android.
updatedOSVersion Is the OS version up to date
deviceBrand Brand of the device
deviceBoard Board of the device
buildUser Build user
buildHost Build host
sdkVersion Sdk version
timeZone Time zone
deviceFaceDown Is the device face down
locationLong Location longitude conditioned by location permission
locationLat Location latitude conditioned by location permission
locationState Location state conditioned by location permission
wifiSsid Wifi SSID
wifiSsidPermissionStatus Wifi SSID permission status
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.

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


The following is a code sample for native Android apps, which uses all values in the specification above for Detect Unknown Sources:


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.



Using Appdome, there are no development or coding prerequisites to build secured Android Apps by using Detect Unknown Sources. 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 Detect Unknown Sources

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:

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.

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