If the prevalence of abusive Google Play apps has left you numb, this latest report is for you. Carefully concealed adware installed in Google-approved apps with more than 440 million installations was so aggressive that it rendered mobile devices nearly unusable, researchers from mobile security provider Lookout said Tuesday.

BeiTaAd, as the adware is known, is a plugin that Lookout says it found hidden in emojis keyboard TouchPal and 237 other applications, all of which were published by Shanghai, China-based CooTek. Together, the 238 unique apps had a combined 440 million installs. Once installed, the apps initially behaved normally. Then, after a delay of anywhere between 24 hours and 14 days, the obfuscated BeiTaAd plugin would begin delivering what are known as out-of-app ads. These ads appeared on users’ lock screens and triggered audio and video at seemingly random times or even when a phone was asleep.