i have been having a problem with the results pages on yahoo lately. this issue is, when i get to the results page, i will hover over a link to a reputable site and the proper url will appearl; however, when i click the link but do not release, the url changes to a yahoo ad link. upon release the click i am directed to an advertised page. To me this seems like trickery because i am intending on going to a site (let ssay wikipedia) and after clicking the url, i am automatically redirected at the last second.. btw im not clicking the "sponsored links".
Yahoo is merging with bing so it's not a surprise. Though what you say sounds like a possible trojan/adware.