Why are emails being sent through my pc to another?

avast email scanner keeps telling me "Caution a potential infection has been spotted" and someone is sending porno emails through my computer to another sender...i have a video on youtube that shows it...the link is here

http://www.youtube.com/watch?v=RxNME_MRt...

i am running avg's rootkit scanner...and i have done spyware and virus scans...is there anyway to stop this?

Why are emails being sent through my pc to another?virus scan

It's doubtful that they're actually running through your computer...unless you're running linux and a mail server on the system. If so, turn off the mail server.

It's actually quite easy for someone to hijack your email address. All they need to know is your email address. If they're running a mail server, they simply compose the email using your email address and drop it into the outgoing mail folder. Then out it goes....