We just found simple trick and also fast way to remove Banner Ads from Yahoo Messenger. This trick, we tested, works properly for Yahoo Messenger 8 but not sure in Yahoo Messenger 9. The trick is:
Don’t Install Flash Player in Yahoo Messenger
Yeah, without Flash Player, the Ads that usually had Flash Format File would never appear again. Ads in Webcam, Chat Room, Yahoo Messenger Window, and also in others part of YM, would disappear instantly without need tweaking or even downloading Yahoo Advertisements Remover or Blocker.