Security experts are warning of the emergence of the world's first computer virus to spread via mobile phones.

The Cabir worm, which has not been released in the wild, affects phones using the Symbian operating system and spreads via Bluetooth, which has a range of about 30 metres.

Infected phones display the message 'Caribe' when turned on, and the worm then looks for other Bluetooth connected handsets nearby that will allow it to spread. Switching off Bluetooth can block the worm.

"From what we know so far we are not aware of any malicious payload," said David Emm, senior technology consultant at antivirus firm Kaspersky Labs.

"It is difficult to say if this will be followed by a spate of such threats, or if hackers will be slower to pick up on this.

"But it is a good example of how we are all carrying a lot more technology that can broadcast [data]. It's a kind of network promiscuity."

The virus was sent to Kaspersky anonymously but seems to be the work of the group responsible for Rugrat, the first 64-bit virus that was identified last month.

The group specialises in 'proof of concept' viruses that do not damage systems.

However, it is not the first virus to target mobile phones. A computer-based virus was identified in June 2000 that sent unwanted text messages to mobile phones.

The virus, called 'I-Worm Timofonica' or 'VBS Timofonica', was a VBS worm that used Microsoft Outlook to spread in a similar way to many subsequent viruses.

A spokesman for Symbian said that, while the company was looking into the case, it would be unlikely to require remedial measures as users had to accept data before the worm could be transmitted.