Just as Bill said this isn't really problem and won't affect you at all. I am trying to see which one of the thousands of links is now redirecting to mediaplex.com because there is no link directly to that site. Every now and then good domains can expire and then get bought up by spam sites. It can just be very hard to quickly track down which link that may be.
I have seen the McAfee warning and the problem is not a virus at that website but some downloads there are considered to be adware or spyware. Like Bill said if you ever do find a link takes you to mediaplex.com just leave it and don't download files from it ( but do let me know the link that took you there ).
This will most likely be a link on one of the many link listing pages here and is not related to the forums at all.
[This message has been edited by Nigel (edited 09-14-2007).]