A mobile phone worm propagating through the phone numbers of users' address books is spreading in the wild across popular SymbianOS smartphone devices, security vendor Fortinet has warned.

According to Fortinet, the worm, dubbed SymbOS/Beselo.A!worm, spreads under the guise of several multimedia file names including Beauty.jpg, Sex.mp3 or Love.rm.

“This particular worm has been found spreading across a number of mobile phones' networks worldwide,” said Nelson DaSilva, regional systems engineer at Fortinet.

“In the last few years we’ve seen worms that are more annoyances than anything else that go through and reset phones to factory defaults or delete all the contacts in your address book.

“However, this particular worm will harvest the user’s contact address book and start resending that same worm to everyone in the address book,” DaSilva said.

Furthermore, it's spreading via Symbian’s S60 operating system, most commonly used in popular smartphone models including Nokia, Motorola, Sony Ericsson, Panasonic and Samsung.

The worm carries a SIS-packed (Symbian Installation Source) but does not bear a .sis file extension, said Fortinet, which makes it easier to fall victim to the phone spam messages.

DaSilva said it’s quite early to tell how rampant the threat has become and Fortinet's research teams are still tracking the data.

Additionally, the Beselo worm sends itself to generated numbers in China, the reason for this is yet to be known, said Fortinet.

According to Symbian, by early 2007, the vendor had shipped over 100 million S60 installed devices around the world.

Users should check their MMS outbox for unrecognised sent message to see if they’ve been infected, said Fortinet.

Symbian US are yet to respond to calls for comment.