Just to followup on the info already given, many viruses these days contain their own mail software, which enables them to self-propagate. They steal email addresses from whereever they can find it on the infected system (the Outlook addressbook is, of course, the favourite) and use them as both the set of recipients for further infection attempts,
and as a list of
forged send addresses.
Somebody else, who just happened to have your email address, got infected, probably by Sobig-F.
That system started emailing losts of other people copies of the worm, some of which will have had
your email a ddress forged in them. Hence you get bombarded with messages from any recipient who has got AV software on their mail system (and there's nothing that you can really do about it
)
All pretty eveil, huh
