A new mobile virus, referred to as the Beselo worm, has several security firms concerned about Nokia smartphones getting infected. One such firm, SMobile Systems, said it has issued a disinfection tool to contain the virus.

F-Secure, an anti-virus and intrusion prevention provider, first posted an alert regarding the virus in its blog last week. The virus is said to affect smartphones running the Symbian S60 Second Edition operating system.

The Beselo worm disguises itself under common media file extensions and misleads users into thinking that they're receiving a picture or a sound file instead of a Symbian application, according to F-Secure. The files sent by the virus are named beauty.jpg, sex.mp3, and love.rm.

F-Secure advised anyone receiving a media file with one of those names to answer "no" to any installation prompt that requests a user to open the file. Image file shouldn't ask installation questions on the Symbian platform and if they do, they should be deemed suspicious, F-secure said in its blog post.

The firm also recommended downloading its anti-virus program for S60 smartphones.

SMobile warned about the same virus on Monday and offered its own anti-virus update and disinfection tool, as part of its Security Shield platform for S60 smartphones. Currently the Beselo worm targets Nokia 6630, 7610, 6680, and N70 smartphone models, said SMobile.

SMobile further described the effects of the virus, saying that when it's installed on a phone, it gathers all the phone numbers located in the phone's contact lists and targets them with a viral multimedia message carrying a Symbian Installation Source version of the virus. Beselo also sends itself to the phone numbers.

The majority of mobile viruses discovered by security firms are considered proof-of-concept, meaning they weren't released into the wild and therefore aren't a widespread threat. However, that's changing with the proliferation of mobile phones, their improved functionality, and increasing use.

SMobile said Beselo is different from any proof-of-concept virus so far.

"This is one of the most advanced viruses to date. It uses MMS and Bluetooth to spread. This virus is similar to a Commwarrior virus that hit in 2005, which we've seen multiple variants of. This shows it's still evolving and in the wild globally. This one isn't actually a Commwarrior variant; it's a new family with more advanced features," said George Tuvell, SMobile's CTO, in an e-mail.

Commwarrior is another virus that targets Symbian S60 smartphones, spreading through Bluetooth and MMS. Phones infected with Commwarrior search for other phones within their Bluetooth wireless range to send malicious SIS files to.