Fencer: Are the banners hosted on BK or on third party hosts? Can the advertiser change the banner after you approved it? Or the server be reconfigured to redirect to certain pages when certain files are requested?
anybody: If it really is a banner on BrainKing causing it, can you identify what banner(s) were present on the page when you were redirected?
How come there's only a few people complaining about it when there are thousands seeing these adds? Maybe there's some other external factor involved (like having spyware or addware on the computer, as has been suggested already).

(I don't have adds activated and really don't plan to, so I won't be answering any of these questions )</b>