I think the said friend was worried about whoever this hacker is, or whatever this virus is, having access to sensitive info that's held on PC's. Such as bank passwords, account numbers, paypal passwords and other such nice things that dishonest people would cream over.
Worst case, there's a keylogger on your pc, logging everything you type, and with this they get passwords to msn, account numbers, bank and paypal and other niceities.
Most probable scenario is, as was previously said, there's a trojan on your system spreading itself through your address book. Get rid ASAP, Norton is nice, as well as those above mentioned freebies i.e. AVG/AGV i forget lol.
Just run a thorough scan, quarentine the blighter and go about having fun on the net. If there's something more about it, such as money going missing, change all your passwords for everything on a different, secure system and conctact your bank's fraud unit to have the money credited to your account.
-Corpo