I’m going to assume that the fact that some Yahoo search results that point to Google with a malware warning are a sign that their new partnership with McAfee just needs a little tuning. The alternatives are either (1) Google is serving Malware, or (2) Yahoo or McAfee are playing a little joke.
Most results that point to Google don’t have this “feature,” and given the recent love fest between the two companies, the joke angle is probably out. Keep an eye out on this query though. I wouldn’t be surprised to see flags popping up all over the place on that page.