Experts at Finnish antivirus outfit F-Secure have this week encountered a cross platform worm that is capable – at least theoretically – of spreading from a PC to a mobile device and back.

The antivirus firm said that the Mobler worm, also known as Cardtrap, is capable of moving between Symbian and Windows platforms.

“Although it’s quite nasty on the Windows side, it doesn’t cause much harm on the Symbian device. It just copies itself to the memory card and tries to trick the user into infecting his PC,” the company said.

On the Symbian side the damage is limited because technically there is no automatic spreading mechanism allowing Mobler to copy itself from one platform to another. The malware simply creates a Symbian installation package that inserts a Windows executable on the mobile device’s memory card.

However, this executable is visible as a system folder in Windows Explorer, so it is possible for the user to accidentally open the executable and infect their PC while browsing files on the memory card.

F-Secure believes that virus writers could use Mobler as a blueprint for more malicious malware that is capable of jumping between platforms. But then again, previous cross platform viruses have thus far failed to cause any significant damage.