WHY would they? i have no clue...but sadly, they do. You were most likely infected from an url you clicked on or something you downloaded. There are a few that do this, so its hard for me to give you an easy fix. But, fix it you have to.
You will need to do a virus scan (be sure you have updated your virus scanner). Since not all scanners will find IRC type trojans, try one of the free online scanners as well http://www.antivirus.com/free_tools/
is a good one, altho it was down when i checked a couple days ago. http://zine.dal.net/previousissues/issue19/letter-from-the-editor.php
gives other resources. On DALnet, the nice ops in #nohack can help you, as well as their website, www.nohack.net
Altho for some wierd reason i cant get it to open, others can, so check http://www.mirc.co.uk/help/virus.html
/me is just an electronics bermuda triangle *sigh*