Android users: Beware when downloading apps from non-authorized, third-party app developers. Angry Birds: Space, the latest installment of the wildly popular mobile game by Rovio, is being used to disguise malware, warn security experts and Rovio.

On Thursday, April 12, security firm Sophos analyst Graham Cluley announced on the company blog that the firm had discovered fake versions of the game, lurking in unofficial app stores. The fake versions contain a "Trojan horse" virus. Also on Thursday, Rovio posted a warning on its own blog, advising users to watch out for fake versions of Angry Birds and urging them to download the new installment from the official store.

Trojan Masked in Fully Functional Version

According to the Web security firm Sophos, the Trojan horse discovered in a file called Andr/KongFu-L, seems to be a fully functional version of the game. However, it installs a virus on the user's Android device, be it a smartphone or a tablet. The code then tries to install even more malware on the infected device, by communicating with a remote Web site. The virus apparently hides its payload at the end of a JPEG image file.

"It feels like we have to keep reminding Android users to be on their guard against malware risks, and to be very careful, especially when downloading applications from unofficial Android markets," said Cluley.

Use Only Official Sources

Although Google allows Android owners to download programs from both official and unofficial sources, security experts advise them to use the official Android Market (now Google Play) to avoid downloading fake apps and potentially malicious programs.

Angry Birds: Space was released on March 22 for Android devices, iPhones, iPads, Macs and PCs. In just three days it reached a whopping 10 million downloads, and 20 million downloads within a week, according to Rovio. Since its release in 2009, Angry Birds has become the most popular paid mobile app of all time. Last year, it exceeded 300 million downloads, across multiple platforms.

The immense success of the game has allowed Finnish developer Rovio to build an entire empire on the franchise, offering everything from plush Angry Birds dolls to comic books and animated videos, and even cookbooks.

(reported by Alexandra Burlacu, edited by Surojit Chatterjee)