Elizabeth,

I have had similar problems with my web domains - these spammers or malign hackers send out mail which purports to be from a genuine domain - but without the permission of the real owner. The negative effects of this are that :-
a) Your reputation may be possibly damaged
b) Your normal email operations from that domain may be hampered. I had a problem in that AOL treated all emails from one of my domains as spam as someone had hijacked it for a while - and all my genuine emails to people with AOL email addresses were barred as being spam for a time

There seems no way around this apart from advising your own ISP that this is happening and most important making sure that you have good antivirus protection and a firewall operating on your PC. Do not open any message with an attachment unless you are sure you are safe!!!

cheers

John