Ad plugin, found in hundreds of Google Play apps, uses well-honed techniques from malware development to hide itself. Ad module forcibly displays ads on the user s lock screen, triggers video and audio advertisements (even while the phone is asleep) and displays out-of-app ads in other areas too. Ad plugin was bundled with 238 unique applications that have racked up millions of downloads between them all from one company in China, CooTek. Google has removed the adware from all the apps on the Play store although users with the apps already installed are still likely to be affected.
Source: https://threatpost.com/android-completely-obnoxious-pop-ups/145390/