An anti-virus firm has found a worm that spreads over mobile phone networks.

Kaspersky Labs said that the Cabir worm infects phones running the operating system Symbian. It spreads over Bluetooth phones disguised as a security tool, but when triggered causes phones to displays the word "Carbre".

The worm forces the operating system to start Cabir when the phone is switched on. It then tries to send itself to other Bluetooth enabled phones.

Earlier this year, Bluetooth vulnerabilities were discovered in Nokia and Ericsson phones that use Symbian.