I work with a large PPC advertiser and they are barely using Yahoo due to poor performance. They tell me they can't identify which which clicks/visitors are coming from Yahoo so I cannot really generate a list of domains to have Yahoo block. Any advice on how to come up with a list? Are there certain domains that are notorious across all business to consumer verticals? If so I'll ban those sites.
It can be futile to fight it because the fraudulent domains keep rotating. It's been the way they get around the 250 domain limit. Since Yahoo! doesn't care about click fraud, it's almost a lost cause trying to fight this.