It's a rare person who would suggest that any online traffic report is completely accurate; most folks know stats from Hitwise, Nielsen, and the like are closer to educated guesses. But it turns out that last month, comScore got Yahoo's June stats wrong by a significant margin, leading Yahoo to announce the problem in a press release today.
It's hard to characterize Yahoo's response as an overreaction; by its own admission, comScore really was way off the mark. Yahoo explained that the organization "underreported Yahoo!'s U.S. page views by more than one billion and its duration metrics by more than 850 million minutes."
So now, "Based on the corrected numbers, on a month-over-month basis, Yahoo!'s U.S. page views were down 4.7 percent versus the reported 7.4 percent, and U.S. duration was down 4.3 percent versus the reported 6.4 percent."
And you can see an even more detailed breakdown below.
comScore, meanwhile, has promised that it's identified and corrected the problem behind these inaccuracies. Yahoo has gone on the record saying that it still has confidence in comScore's figures, too.
Hopefully everything will be back to normal by the time comScore's stats for July roll in, then.