At least two million Google Play downloads gave Android users an unwanted freebie in the form of BadNews, a piece of malware which masqueraded as a legitimate advertising network.
The malware was integrated into 32 different apps in the Google Store, according to mobile security specialist Lookout. Those apps have been downloaded more than two million times, exposing users to embedded advertising - but the ads then push users towards fake app updates - which in turn send out premium-rate SMS messages via the well-known AlphaSMS malware.
BadNews, as the malware has been dubbed by Lookout, slipped by Google's automated detection by posing as a legit advertising network. Such networks fund free apps by supplying standard-sized advertisements, and thus it shows ads for other applications by the same authors.
After phoning home to the authors' command-and-control servers, BadNews displays "essential" updates for the popular Russian social network Vkontakte's app, as well as Skype's app. Both of these "updates" lead directly to known infected files.
Those infections are APK files so the user still has to agree to the installation, which will be blocked by Lookout (or your other security software of choice). One could argue that that's hardly worse than the entirely legitimate embedding of links to premium-rate numbers, which don't even trigger a warning dialogue box, but BadNews does demonstrate how malware authors are gaming the system.
That system starts Google Bouncer - Google's automatic app taste test, which is supposed to weed out malware before it gets listed. However, five minutes of automated testing won't spot this kind of scam, so Android depends on the wisdom of the masses.
It is not clear whether some or all of these apps were launched with the explicit intent of hosting BadNews or whether legitimate developers were duped into installing a malicious advertising network. However, based on our analysis of the backend code behind a number of these purported ad networks there is little doubt that BadNews is a fraudulent monetization SDK.
Malware apps are quickly identified by the first user who gets burnt. The user (hopefully) shares the experience and prevents further infection of unwitting users, which is why BadNews is such a significant development. Once installed the new malware simply polls a command server every four hours, sending back the user's phone number and IMEI, which means the malware's authors can rack up some positive feedback on Google Play before triggering the infection once the software is widely installed.
For users that just means being more wary of peer reviews, and remembering not to install anything which looks dodgy. Users who doubt their ability to judge apps' potential dodginess should probably install some security software too, or switch to a platform less targeted by malware authors. ®