How to avoid having my app shown in the list of recently used apps in Android
You have to add android:excludeFromRecents="true" to the activity in your AndroidManifest.xml
Sample code:
<activity
android:label="@string/your_app_name_goes_here"
android:excludeFromRecents="true"
android:name=".SomeActivityNameGoesHere" >
<intent-filter >
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>