A new virus that can move from a mobile phone to a PC has come to light.

Security researchers reported first sightings of the Trojan program yesterday. It masquerades as pirated software for mobile phones and attempts to infect PCs via the phone's memory card.

It is not considered to be a significant risk but is the first attack seen that tries to use a mobile phone as a jumping off base. "From a more academic point of view it's very interesting," said Mikko Hypponen, director of anti-virus research at F-Secure.

Anti-virus vendor Trend Micro has rated the Trojan, called Sybos/Cardtrap.A, "low". It includes a variety of malicious programs, including a number of viruses that spread from phone to phone via Bluetooth or MMS. It affects mobiles running Symbian Series 60 and Windows.

The Trojan attempts the jump to PCs by copying two Windows worms to the mobile phone's memory card. A user who then inserts this card into a PC and clicks on one of the infected files will launch a worm that attempts to spread to other PCs on the network.

Mobile phone attacks have been on the rise, though not nearly as widespread and disruptive as PC worms and viruses. F-Secure estimates that 28 countries have now reported instances of the Cabir worm, which uses Bluetooth connections to spread between Symbian-based phones. Another Symbian worm, called Commwarrior, has been sighted in 19 countries, Hypponen said. Commwarrior can spread via Bluetooth or MMS messages.