Dozens of Android camera apps with over 1 million installs on the Google Play Store were serving malicious ads and fake update prompts. Some of the apps allowed users to apply photo filters on their snapshots. The apps have all been removed from the store by now, but not before they were able to amass millions of installations. After installation, they would automatically hide from the application list to make sure they won’t be uninstalled by hiding their entries from the app list. They would then start displaying adult content and fraudulent content ads using the default web browser.
Source: https://www.bleepingcomputer.com/news/security/android-apps-with-millions-of-installs-collect-selfies-push-porn-ads/