It's sneaky and destructive, warns Symantec...
Symantec has issued a warning that describes a destructive new trojan horse called Trojan.Zeraf.
Symantec says the trojan can delete a large number of system files, preventing PCs from running Windows and stopping PCs from rebooting off the hard drive.
The safest way to deal with the trojan is to completely reinstall Windows. The trojan is triggered by opening the .exe file that carries it into the system.
Andre Post, senior researcher at Symantec, said: "The notable thing about this trojan is that it is so highly destructive. It is also impossible to recognise before opening it because the file can simply be renamed by the sender."
However, the chances of being hit by the trojan are slim - so far Symantec has only received one report of it in the wild, and it does not attempt to reproduce itself.
Symantec also re-issued a warning about a worm called W32.HLLW.Bymer. It was first noticed in October 2000 but has recently resurfaced.
The worm is relatively harmless, seeking only to install a program enabling peer-to-peer working on the victim's PC, but it can impair PC performance.