If you’ve got an Android phone, you might want to check it right away.

Security experts have found 12 popular apps infecting phones with annoying adware, that bombard mobile screens with annoying sponsored messages. While this may sound more annoying than concerning, this type of scam can end up generating huge sums of money for cyber crooks while clogging up phones with content people never agreed to see.

What’s worrying about this latest attack is the number of downloads some of these apps have had, and how the criminals behind them are hiding their tracks, reports the Mirror.

One app, Super Skibydi Killer, has been downloaded more than a million times, while another, Agent Shooter, has been installed on around 500,000 devices. Some of these apps use sneaky tricks to hide themselves on devices, so users often forget they’ve ever been installed.

Besides the irritating adware scam, some of these apps have also been found to push users towards risky investment scams and dodgy casino sites. All these apps were available on Google’s Play Store but have now been banned by the US tech giant.

Although the apps can’t be downloaded anymore, if you’ve already installed them, now is the time to remove them to keep your device safe. Here are all the apps found by specialists at IT-security solutions website, Dr Web, and how many times they’ve been downloaded.