Are you referring to an installation you had made, or one that seemed to have gotta on your computer without your concent? There are two--one from this site (clean, no virus/trojan/etc) and then one that appears on your computer misteriously (Virus/trojan).
For the real morc, you can follow these steps:
1. Goto your start menu, and click control panel. A window will appear.
2. If you have XP, click "switch to classic view" on the left hand side. The icons will change, where there you can locate "Add/remove programs".
3. In the list preceding, locate "mirc" and click the remove button on the right hand side of that row.
4. Follow the simple instructions, and viola!
Easy as pie. As for the virus/trojan/idk_how_the_---_mirc_got_on_my_computer version, you may try looking
Here On that page, ParaBrat has a nice message, then click the link rogue provided, and that should help you out.
