In a blog post, Lookout security intelligence engineer Kristina Balaam said the plugin, which had been named BeiTaAd, forcibly displayed ads on the locked screen of a device, triggered video and audio ads even while the phone was asleep and brought up out-of-app ads that got in the way of an individual interacting with other applications.
Lookout found this plugin in 238 separate apps and reported the matter to Google which had now removed the plugin from all affected apps, Balaam said.
"Cumulatively, these applications amount to more than 440 million installations, making this family unique in its prevalence and the level of obfuscation used to hide the plugin’s existence," she said.
All the apps which had the plugin were from the mobile Internet firm CooTex which is based in Shanghai. The company is listed on the New York Stock Exchange and its best-known app is the keyboard app TouchPal.
"The BeiTaPlugin package, com.cootek.beita.plugin, is unsurprisingly bundled within TouchPal as well as numerous add-ons to their popular TouchPal keyboard, and several very popular health and fitness apps," Balaam said.