Why didnt advast prevent this?
you mean avast.
how do you read your mail?.....webmail (reading in your web browser) or do you download the mail to your computer with a mail client like outlook / outlook express....
webmail: your account may be hacked .... try change your password
mailclient: you may have a infection.... check for infections
or they just harwested a bunch of addresses, and the sendt from address faked
it can also be that any of your friends computers is infected and your mailaddress was in there address list