(CNN) -- Update: GoDaddy says hackers are not to blame for the service outage.
GoDaddy, the massive Web hosting company, went down for several hours on Monday, taking an untold number of websites with it.
A person affiliated with the hacking collective Anonymous -- named @AnonymousOwn3r on Twitter -- claimed responsibility for the outage.
"I'm taking godaddy down bacause (sic) well i'd like to test how the cyber security is safe and for more reasons that i can not talk now," that person wrote in response to questions from a technology reporter at tech blog Mashable.
The attack appeared to take down websites that use GoDaddy servers to host their information and also those that have registered their names with the company.
By Monday night, however, the company, which says it is the "largest hosting provider of secure websites in the world," said most of its sites were working again.
"Most customer hosted sites back online," GoDaddy said on Twitter. "We're working out the last few kinks for our site & control centers. No customer data compromised."
The outage caused widespread Internet problems on Monday.
"The more problematic part is that any domain registered with GoDaddy that uses its nameservers and DNS records are also down," Mashable wrote. "That means that even if you host your site elsewhere, using GoDaddy for DNS means it is inaccessible."
The company, which says it hosts 53 million domain names, has not commented on the cause of the problem.
"It is not just your site," one apparent GoDaddy client wrote in response to the company's tweets. "It is EVERYTHING anyone has hosted with you.... from e-mail to websites...."
GoDaddy also apologized to its customers.
"So many messages, can't get to you all... Sorry to hear all your frustration," the company said on Twitter. "We're working feverishly to resolve as soon as possible."