F-Secure is currently investigating a new trojan infecting Symbian Series 60 phones - Skulls. Unlike Cabir, this trojan is actually malicious. Symbian must have anticipated this, having recently signed for McAfee's virus protection.
This trojan [SymbOS/Skulls] has been distributed on Symbian shareware download sites as "Extended Theme Manager" by Tee-222. If you see it, don't install it on your phone. It will make you're phone useless and it will prevent it from booting up. Recovery could get tricky, especially if you don't have a third-party file manager software already installed on your phone. The most obvious symptom of the trojan is that the typical programs on the phone won't work any more, and that their icons get replaced with a a picture of a skull.
