comScore off by a billion page views on Yahoo's popularity

Yahoo decided to announce the error itself and discussed that choice in its announcement.

"We issued this release because it's important that our business partners, advertisers and shareholders have an accurate, independent third-party measurement of our performance," Carol Bartz, the chief executive of Yahoo, said in a statement.

She added that "we believe comScore is committed to addressing the error and ensuring accurate and reliable reporting of marketplace performance. Yahoo! is fully prepared to work collaboratively with comScore to develop policies and practices to ensure the timely correction of inaccurate information."

On the company blog, comScore said it "was an isolated, one-time error that did not affect any other client’s data," according to Linda Boland Abraham, executive vice president for marketing.