The hacker attacks that shut down Twitter and hobbled Facebook Thursday appear to be the result of an assault on the social-networking sites of an activist from the former Soviet republic of Georgia, Facebook said.

Twitter and Facebook each said they are working to prevent further denial-of-service attacks after Thursday’s onslaughts tripped up both sites.

The activist had accounts on Facebook, Twitter and YouTube, as well as the LiveJournal blogging site, which also was hit.

With denial-of-service attacks, hackers take control of thousands of computers, creating so-called botnets. They then send massive amounts of data to one Web site, causing it to slow down or crash.

While the attack may have only been intended to hurt one person, the social-networking sites themselves were “collateral damage,” said Dmitri Alperovitch, vice president of threat research for security-software maker McAfee.

“The problem with these attacks is knowing who waged them is so difficult,” Alperovitch said. “The botnets launching the attacks were all over the world.”

The blogger’s nickname is Cyxymu, another spelling for the capital of Abkhazia, a breakaway part of Georgia.