Virus lynchpins are distributing an Android Trojan under the guise of popular photo-sharing app Instagram.

The fake version of the Instagram Android app is being distributed via unapproved sources, rather than official sites such as the Google Play Android marketplace. The rogue app has been published on a Russian website purporting to be an official Instagram site, among others.

Once installed, the app will silently send SMS messages to premium rate services, doubtless earning its creators a tidy commission at the expense of fandroids in the process.

Cybercriminals are seeking to exploit the popularity of the Instagram app – which has millions of users around the world, prompting Facebook to pay an eye-watering $1bn for the firm behind the technology earlier this month.

Security firms including Sophos, which detects the malware as Andr/Boxer-F, have added detection for the malware to their smartphone security suites. The Instagram Android Trojan represents the latest example in a growing number of viral threats to target the Android smartphone platform.

"Android malware is becoming a bigger and bigger problem," said Graham Cluley, senior technology consultant at Sophos. "Just last week, we saw a bogus edition of the Angry Birds in Space game and it's quite likely that whoever is behind this latest malware is also using the names and images of other popular smartphone apps as bait.

"Infected Androids are now effectively part of a botnet, under the control of malicious hackers. Android users need to be extremely careful when downloading applications from sites, especially when they're not official Android markets."

Curiously, the malware contains a random number of identical photos of a man. The photo features a cropped image of a casually dressed witness from a Moscow wedding photo, an image that has become something of a phenomenon on Russian internet forums.

More information on the Android Instagram threat can be found in a blog post on Sophos's Naked Security website here. ®