Downloading apps from non-official sources potentially places users at risk, but Google Play Store malware infected apps do exist. Google has controls in place to prevent malicious apps from being uploaded to its app store, but those controls are not always 100% effective. Choosing to download apps only from official stores is no guarantee that the apps will be free from malware.

Security researchers recently discovered around 300 apps offered through the Google Play store that appear to be legitimate programs, yet are infected with malware that add infected devices to a large botnet. The botnet was being used to launch distributed denial of service attacks (DDoS) on websites.

The botnet, dubbed WireX, comprises of tens of thousands of Android devices that are being used in highly damaging cyberattacks. Devices started to be infected in early July, with a steady rise in additions over the following weeks. Even though numbers of compromised devices grew steadily in July, the botnet was only discovered in early August when the WireX botnet started to be used in small scale DDoS attacks.

Since then, larger attacks have taken place, mostly targeting the hospitality sector. Those attacks have clogged websites with junk traffic preventing legitimate users from accessing the sites. Some of WireX DDoS attacks involved as many as 160,000 unique IPs. Since devices could conceivably be used to attack websites with multiple addresses, the size of the botnet has been estimated to be around 70,000 devices.

The growth of the botnet was soon attributed to malicious apps, with researchers discovering around 300 Google Play Store malware infected apps. Google has now disabled those apps and is in the process of removing them from devices.

The apps included video players, battery boosters, file managers and ringtones. The apps were not simply malware, as users would undoubtedly attempt to delete the apps if they failed to perform their advertised functions. The apps all worked and users who downloaded the apps were unaware that their devices were being used for malicious purposes. The malware used a ‘headless browser’ which was able to perform the functions of a standard browser, without displaying any information to the user allowing the actors behind the malware to operate undetected.

When the devices were needed for DDoS attacks, they would receive commands from their C2 server to attack specific websites.

Multiple security vendors including Akamai, RiskIQ, Flashpoint and Cloudflare collaborated and succeeded in taking down the WireX botnet. Without that collaboration, the botnet would still be active today and may not have been detected.