An interesting phenomenon is occurring within Yahoo Search Marketing that has been expressed pretty intensely by affected advertisers at WebmasterWorld. According to the impacted advertisers, the quality of their campaigns have gone down because of false impressions that have been generated for long tail keywords that were often never searched upon. In the case of one advertiser, his ad campaign served nearly 120,000 new impressions (triple what it was before) because of these obscure keywords in the campaign. After digging into his statistics, he disabled these low-performing keywords, but the damage had already been done, and the overall campaign effectiveness was reduced.
In other words, "a competitor found a low traffic keyword that [was being] advertise[d] on and searched tens of thousands of times to skew your CTR, thus lowering the quality of [the] entire campaign."
Only two Yahoo PPC users have been impacted by this shift thus far. According to one Yahoo rep, it is probably due to "market fluctuations," but typically, those who run the campaigns themselves would be most abreast of any market fluctuations (am I right?) It seems, to both affected individuals that there may be something else going on here, perhaps in the sense of fraud.
Forum discussion continues at WebmasterWorld.