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This advertisement provided by GoDaddy.com shows a scene from their commerical featuring Colombian model Natalia Velez. The web host went down Monday afternoon. (GoDaddy.com/Associated Press)

Thousands and possibly millions of web sites hosted by GoDaddy.com are down, and a hacker is claiming responsibility, but the real reason for the outage is unclear. 

A Twitter feed allegedly affiliated with the "Anonymous" hacker group says it's behind the outage, but another Twitter account associated with Anonymous says the first one is just taking advantage of an outage it had nothing to do with.

GoDaddy.com hosts more than 5 million websites, mostly for small businesses. Websites that were complaining about outages on Twitter included MixForSale.com, which sells accessories with Japanese animation themes, and YouWatch.org, a video sharing site.