Several new types of pre-installed malware are targeting critical system apps on mobile devices, making them difficult to remove.

Researchers at Malwarebytes came across two instances of pre-installed malware targeting applications in /system/priv-app/, where critical apps such as settings and system UI reside. The first infection occurred on a THL T9 Pro device. The malware repeatedly installed variants of Android/Trojan.HiddenAds, which is known for displaying lock screen advertisements that take up the device’s entire screen. In this particular case, the infection wrapped itself up in the critical system Android app System UI.

The second infection occurred on a UTOK Q55. In that case, the threat came hardcoded in the device’s Settings app. It fit the “monitor” category of potentially unwanted programs (PUP), which are capable of collecting and reporting users’ information.

The Pre-Installed Malware Problem Persists

These two instances of pre-installed malware aren’t the first detected by Malwarebytes. In March 2017, researchers at the security software provider observed mobile devices manufactured by BLU being shipped out with Android/Adware.YeMobi. Then in December of that year, the researchers found an auto-installer known as FWUpgradeProvider pre-installed on devices bought from legitimate phone carriers in the U.K. and elsewhere.

Other security firms have detected pre-installed malware more recently. For instance, Check Point discovered RottenSys disguised as a system Wi-Fi service; the threat targeted nearly 5 million users for fraudulent ad revenues as of March 2018. A few months later, Avast Threat Labs found adware known as Cosiloon pre-installed on hundreds of Android device models.

How to Protect Mobile Devices From Pre-Installed Malware

Security professionals can protect mobile devices from pre-installed malware and other threats by using a unified endpoint management (UEM) solution to monitor how these devices report to the corporate IT environment. They should also use behavioral analysis to help defend mobile devices against zero-day threats.