Anti-virus vendors have raised an alarm for a new worm squirming through mobile phone networks, using Bluetooth and MMS (Multimedia Messaging Service) to infect Symbian OS devices.

According to F-Secure, the worm was detected in the wild, using social engineering lures to trick smart-phone uers into installing an incoming SIS application installation file. It affects Symbian S60 2nd Edition phones.

The worm, identified as SymbOS/Beselo.A!, has been detected using following file names: Beauty.jpg, Sex.mp3 and Love.rm.

[W]hat makes Beselo interesting is that instead of a standard SIS extension the Beselo family uses common media file extensions. This leads the recipient believe that he is receiving a picture or sound file instead of Symbian application. He is then far more likely to answer "yes" to any questions the phone prompts after clicking on such an incoming file.

F-Secure Senior Anti-virus Researcher Jarno Niemelä said the in-the-wild propagation of the worm was confirmed by an employee at a major (unnamed) telecommunications operator. "It turns out that Beselo.A was in the wild on their MMS network and that it had a big brother, Beselo.B," Niemelä said.

The US-CERT has posted a warning to Symbian S60 users to:

Use caution when accepting incoming files via MMS and Bluetooth.

Secure Bluetooth connections to prevent access from unauthorized devices.

Install anti-virus software and keep its virus signature files up-to-date

Over the last two years, anti-virus vendors have repeatedly warned that smart phones will become a legitimate target of malware, but not everyone is convinced the risk is high enough to justify additional spending on security software.