Skulls trojan targets Symbian smartphones

A new trojan on the internet attacks the Nokia 7610 smartphone and possibly other phones running Symbian Series 60 software.

"We have located several freeware and shareware sites offering a program, called Extended Theme Manager, that contains a trojan," said Mikko Hyppönen, director of antivirus research at F-Secure. "The virus writer is going by the name Tee-222."

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The malicious code, called Skulls, deactivates all links to Symbian system applications, such as e-mail and calendar, replacing their menu icons with images of skulls. Hyppönen said that users of affected phones could only send or receive calls.

Hyppönen said Extended Theme Manager looked "pretty convincing" as a freeware maintenance tool and that many sites had not bothered to verify it or even try it out. Most monitored sites have since removed the program.

When installing the file "extended theme.sis", Symbian phone users are informed by the OS that the software is not Symbian Signed - a trusted program initiated by Symbian - and asked if they want to continue.

"This is definitely a good warning," said Hyppönen, "but the problem is that any advanced PC user who downloads software regularly sees this kind of warning 99% of the time and simply clicks OK."

One way to correct the problem, Hyppönen said, was a hard reset, which restores affected phones to their default factory setting. Unfortunately, all private data, such as phone books and calendars, is lost in the process.

Earlier this year, the Symbian OS was the target of the Cabir virus, which, like Skulls, transmits a .sis file. But unlike Cabir, which scans for accessible phones within Bluetooth range and makes a copy of itself, Skulls is not self-replicating.

John Blau writes for IDG News Service