Experts at security firm Sophos are warning Android phone owners about 22 dodgy apps that drain battery life and could result in a big phone bill.
The Sun reported the "click-fraud" apps pretend to be normal apps on the Google Play Store, but secretly perform criminal actions out of sight.
The 22 apps have been collectively downloaded more than 22 million times.
"From the user's perspective, these apps drain their phone's battery and may cause data overawes as the apps are constantly running and communicating with servers in the background," researchers told The Sun.
Warning signs include increased data usage and fast-draining battery life, however, pinning such issues to a particular app is hard.