Cabir, the Symbian OS and Series 60 UI-targeting malware, is expected to spread significantly in the coming months after the source code was posted on the Internet this week.

Anti-virus software companies has believed that the worm, which was first detected in June 2004, was the work of a tightly-knit virus-writing cabal. However, the code appears to have slipped out and been brought to a wider audience. A number of the more recent versions of Cabir appear to be straightforward recompilations rather than code-tweaks, suggesting that the source code has leaked.

Cabir spreads between mobile phones using a special Symbian operating system file. When the infected file is launched, the mobile phone's screen displays the word "Caribe" and the worm modifies the Symbian operating system so that Cabir starts each time the phone is turned on. Cabir scans the airwaves and sends copies of itself to the first vulnerable phone it finds using Bluetooth technology.

Cabir causes more irritantion than harm. Not directly dangerous to date, the worm nonetheless keeps a handset's Bluetooth radio active, running down the battery more quickly than might otherwise be the case.

Some more recent versions of the worm are able to spread more quickly, having apparently fixed a glitch that limited its ability to disseminate itself. Instead of targeting one phone between handset reboots, the worm will now try to send to other phones, should the first move out of Bluetooth range. ®

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