Fake mail from FBI or Microsoft is really the Sober virus
This virus has fake but compelling messages from the FBI or from Microsoft. Just receiving the message will not infect a computer. A significant number of people have opened the attachment and infected their computers. Instead, delete the email.
Current virus definitions (2/21/05 or newer) will catch this virus. Those who have instituted automatic updates of VirusScan or Norton will be protected. You should be able to clean this virus using an on-demand scan, current virus definitions, and either VirusScan or Norton. The McAfee Stinger tool (ftp://ftp.iastate.edu/pub/antivirus/stinger/stinger.exe) should also be able to remove this virus.