Researchers found a clicker Trojan bundled with 33 apps downloaded by Android users over 100 million times. The malware was designed as a malicious module added to seemingly harmless applications such as audio players, barcode scanners, dictionaries, and a host of other types of ordinary software most people would install on their Android devices. Android.Click.312.origin would only activate 8 hours after the apps that contained the malware were launched to evade detection. Google removed several of the reported apps, while a number of them got updated and had the malicious module removed.
Source: https://www.bleepingcomputer.com/news/security/android-apps-with-over-100m-installs-contain-a-clicker-trojan/