The company, which runs a series of irreverent blogs on media, technology and other issues, said in a posting on its website Sunday that the commenting passwords used on the sites were encrypted, but simple ones could be vulnerable to attacks by hackers' computers.
The company also said passwords on other sites should be changed if they were the same as the ones stored by Gawker Media.
"We're deeply embarrassed by this breach," the posting on gawker.com said. "We should not be in the position of relying on the goodwill of the hackers who identified the weakness in our systems."
Messages were left Sunday night for Gawker chief Nick Denton. Gawker's Gizmodo tech blog gained fame in May when it posted pictures of an iPhone prototype. The phone was lost by an Apple Inc. engineer in a Silicon Valley bar.
The Gawker breach is the latest in a recent series of cyberspace attacks on websites. Last week, the Visa and MasterCard sites were inaccessible for a short time likely because of attacks by supporters of the WikiLeaks website. Supporters were angry that the credit card companies had stopped processing donations to WikiLeaks.
Both MasterCard and Visa said that cardholders' accounts were not at risk and that people could continue using their credit cards.
Supporters of WikiLeaks, which has released thousands of classified government documents in recent weeks, said they would attack companies and groups hostile to the site and its founder. An Internet group operating under the label "Operation Payback" claimed responsibility for the MasterCard and Visa problems in messages on Twitter and elsewhere.