reddo,
Virii always come from someone you know. Computer virii also come from someone you know. The more you trust someone/exchange email with someone, the more likely they are to send you a virus without them knowing. The rule to follow is NEVER open an attachment which has a suffix which runs a micro$oft program (.pif, .exe, .vbs, etc. etc. etc.) Make bloody sure that you have windoze set up to show you the whole filename of attachments.
Mik