I reveiced this same report from Spyware Doctor. Spy Sweeper, Spybot S&D, Kaspersky, Ad Aware and F-Prot reported the same system clean.
I tried this same test on a system without mIRC. It was reported clean. I did a fresh install of mIRC, ran mIRC and then ran Spyware Doctor - it then reported 18 registry keys as an "infection".
The registry keys that Spyware Doctor reports are the DDE keys... This are the keys which alow websites to have links like <a href="irc://server.com/channel" target="_blank">irc://server.com/channel</a>
And when you click on one of those links it auto start mIRC and connect to server.....
Without those registry keys, the DDE will not work.
The reason Spyware doctor doesn't find anything is because mIRC ads the registry keys to your registry only after you start mIRC
Spyware doctor sucks... Adaware if more accurate and you might also consider trying X-Cleaner which is preaty good on finding stuff that others can't.
