SAN FRANCISCO - An unannounced change in the way Alexa.com tracks traffic to websites left millions of site owners wondering why their rankings had changed so dramatically.

 

After users reported shifts in their rankings - in some cases, rankings dropped thousands of spots - Alexa.com announced it had released the "New Alexa Ranking System."

 

The biggest change in the new system is that Alexa no longer relies solely on the Alexa toolbar for traffic statistics. The company said it now collects data from multiple sources to compile its statistics and Web rankings. The company hasn't disclosed which sources it uses.

 

Alexa.com has been under fire in recent months for its methodology, particularly after announcements such as YouTube having more traffic than Google.

 

While the new system is designed to address flaws for which the company has been criticized, a statement at Alexa.com did not confirm nor deny past problems but tried to put a positive spin on the revamp and resulting rank changes.

 

"Your ranking wasn't wrong before, but it was different," the company said. "Alexa toolbar users' interests and surfing habits could differ from those of the general population in a number of ways, and we described some of those possible differences on our website. While the vast majority of sites' rankings were unaffected by such differences, we've worked hard on our new ranking system to adjust for situations in which they could matter. The new rankings should better reflect the interests and surfing habits of the broader population of Web users."