there are several new viri out doing this. very similar to the bagel virus.
W32.MYtob.... vith varients. however symantec does have a cleaner and defs for it.
Description: Trojan.Tooso.F is a Trojan horse that interferes with the operation of security software by terminating processes, stopping services, removing registry entries, and deleting files. This Trojan is similar to W32.Beagle@mm but it does not send emails.
the alert for this one came out on april 16th, and at that time symantec did not have virus signatures for it.
and after a bit of searching:
W32.Beagle.BP@mm is a mass-mailing worm that uses its own SMTP engine to send out copies of a Trojan.Tooso variant. The worm also opens a back door on the compromised computer on TCP port 80.
more info here
First rule of thumb is to never open an attachment from someone you don't know.
Second rule is to run WindowsUpdates. these take advantage of an unpatched system... of course once you open the attachment you become infected. by being patched you prevent it from spreading.
also, regarding email spoofing, a good host (provider of your email) will not allow delivery of messages not sent specifically to you. for example some providers will allow anything addressed to firstname.lastname@example.org. for example bizek88 is getting everything with bizek in the address. Good providers don't allow that. Infact i switched host providers for my website for this very reason.
hope this helps.