It is possible that your friends are sending you a virus without knowing it.
I have fixed my machine with the instructions below.
From: Sydney Harper <sydney_msn at email.msn.com>
To: rcb5 at msn.com <rcb5 at msn.com>
Cc: 'John Reeder' <johnr_msn at email.msn.com>
Date: Saturday, February 13, 1999 11:54 PM
Subject: Re: Neural Networks: Intelligent Systems
>>I just wanted to let you know that you seemed to be infected with the
>Happy99.exe worm. You posted a message to the Artificial Intelligence
>Forum's msn.computingcentral.artificial.intelligence.general newsgroup that
>contained the Happy99.exe worm. This worm/virus infects people by
>replicating itself on every newsgroup and email message you send. For
>example, for every legitimate message you post, another message is posted
>with the same subject except it contains only the happy99.exe file as an
>attachment. You get infected by opening the Happy99.exe file attachment.
>You can get more information on the worm and instructions for deleting it
>from the following web site.
>>http://www.symantec.com/avcenter/venc/data/happy99.worm.html>>I have removed the message containing the happy99.exe attachment. Please do
>not post again in the newsgroup until you have removed the Happy99.exe worm
>from your computer.
>Artificial Intelligence Forum