Email Virus! HELP!

My Dad is using Win. 98SE Eudora email. he can’t send mail. When he tries he gets this message:

, 1 Messages left to send,. MAIL FROM ,agmt@tds.net> [08:05:10 PM] There has been an error tranferring your mail. I said MAIL FROM: ,agmt@ds.net> and then the smtp server [smtp.tds.net said 5:00 Polite people say HELO first

Any idea what this virus is and how to get rid of it?

Thanks!

Karen