Summary

Did you get a message like this?

 
 
        BOOT SECTOR WRITE
        POSSIBLE VIRUS
        Allow (Y/n)?

If so, this is displayed by the BIOS code of your machine. The text is displayed almost always when you try to write to the master boot sector of your machine. This does not necessarily mean you have a virus. You could be using FDISK, Format or disinfecting a virus. If necessary, turn the warning of from your BIOS settings, look for an option like "Virus protection". If you get the message when booting with a floppy in drive A: or when running an unknown program, it is probably caused by a real virus. [Analysis: Mikko Hypponen, F-Secure]