The fact that you mention a McAfee tech indicates you realize that your antivirus software was responsible for the problem. The fact that settings contained in perform.ini and mirc.ini indicates that the AV deleted or quarantined everything in the folder, and they either didn't get restored, or you did a reinstall that overwrote the existing settings. If you search the entire drive for other copies of perform.ini and mirc.ini, and if these files are not in your recycle-bin or your quarantine area, they may need to be recreated from scratch. If you do find multiple copies, hopefully one of them is the right one, based on the timestamp indicating when they were last written to.
The window positions/sizes/fonts are kept in mirc.ini, and it wasn't clear whether they keep on being unset, or whether you're just wanting to get back the original settings. If writes to mirc.ini are having no effect, either you're somehow trying to place them in a folder where you don't have diskwrite permissions, such as c:\program files\, or the firewall settings are really not fixed, and the mirc.ini and possibly other files are getting quarantined. I've even had an AV quarantine the aliases.ini file from a fresh install.