A new Skulls worm affecting Symbian phones has appeared. Unlike its predecessor however, it can spread to other phones.

"What is harmful about Skulls.B is that it can spread to other Bluetooth-enabled phones," said Mikko Hypp"nen, director of anti-virus research at F-Secure. "Skulls.A was bad in that it can wipe out all your applications, including your phone book, but it can't infect other phones."

Trojan horse programs are destructive and can modify the configuration of PCs but typically do not attempt to infect other machines like viruses and worms.

Although containing similar programming to its predecessor, Skulls.B doesn't replace the menu icons of Series 60 phones with images of skulls and crash e-mail and SMS applications. No, it uses jigsaw puzzle pieces but with exactly the same effect.

To be infected however, requires user interaction. You need to press the Skulls.B icon in the menu to active the Trojan, according to Hypp"nen. A programming error prevents the virus from automatically running after installing itself on the phone, he said.

Discovered earlier this year, Cabir is a proof-of-concept worm that uses the Bluetooth protocol to copy itself onto devices around 30 feet away. It is transmitted as a Symbian installation system file and disguised as a security utility, called Caribe.

The Cabir worm drains a phone's battery relatively quickly because it is constantly trying to locate and connect with other Bluetooth-enabled devices, according to Hypp"nen.

F-Secure conducted tests on Series 60 smart phones from several vendors, including Nokia, Matsushita (Panasonic), Sendo and Siemens. All but one model, Siemens SX1, proved vulnerable, according to Hypp"nen. "I can't explain why the Siemens phone is immune to this virus but it is," he said.

F-Secure advises users of Series 60 smart phones to set their handsets into non-discoverable (hidden) Bluetooth mode.