Following analysis of attacks on mobile devices, Kaspersky has uncovered that 14.8% of its users who were targeted by malware or adware in 2019 suffered a system partition infection, making the malicious files undeletable. Moreover, research found that pre-installed default applications also play a role. Depending on the brand, the risk of undeletable applications varies from one to five percent in low-cost devices, and reaches 27% in extreme cases.

A system partition infection entails a high level of risk for the users of infected devices, as a security solution cannot access the system directories meaning it cannot remove the malicious files. According to Kaspersky researchers, this type of infection is becoming a more common way to install adware via software created to display intrusive advertising. Infection can happen via two paths: the threat gains root access on a device and installs adware in the system partition, or the code for displaying ads gets into the firmware of the device before it even ends up in the hands of the consumer.

Among the threats uncovered in the system directories, Kaspersky found a variety of malicious programs from Trojans that can install and run apps without the user's knowledge to less threatening, but nevertheless intrusive, advertising.

In some cases, adware modules were pre-installed before the user even received their device, which could lead to potentially undesired and unplanned consequences. For instance, many smartphones have functions providing remote access to the device. If abused, such a feature could lead to a data compromise of a user's device.

"Our analysis demonstrates that mobile users are not only regularly attacked by adware and other threats, but their device may also be at risk even before they purchased it," said Igor Golovin, security researcher at Kaspersky. "Customers don't even suspect that they are spending their cash on a pocket-sized billboard. Some mobile device suppliers are focusing on maximizing profits through in-device advertising tools, even if those tools cause inconvenience to the device owners. But this is not a good trend, both for security and usability. I advise users to look carefully into the model of smartphone they are looking to buy and take these risks into account. At the end of the day, it is often a choice between a cheaper device or a more user-friendly one."

For more information, read the full report on Securelist.