Aug. 7 (Bloomberg) -- Twitter Inc. and Facebook Inc. are working to prevent denial-of-service attacks, a day after an assault on a blogger’s social-networking accounts hobbled both sites.

Yesterday’s attacks targeted an activist blogger from the former Soviet republic of Georgia, Facebook said. The user had accounts on Facebook, Twitter, YouTube and LiveJournal Inc. Google Inc.’s Blogger, which also was hit, said some users were still having problems connecting this afternoon.

With denial-of-service attacks, hackers take control of thousands of computers, creating so-called botnets. They then send massive amounts of data to Web sites, causing them 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 Inc.

“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, he said.

Defense Measures

Twitter’s defense measures have caused some disruptions today, the company said. Many users couldn’t send their updates, known as Tweets, via short messaging service and other applications, San Francisco-based Twitter said.

“In the past 24 hours, we’ve been contending with a variety of attacks that continue to change in nature and intensity,” Biz Stone, co-founder of Twitter, said in a blog. “We can and will improve system response to these assaults such that they don’t interfere with our normal, everyday Twittering.”

A denial-of-service attack shut down Twitter entirely yesterday, while the Facebook disruption only affected some users. Both sites resumed service later in the day, as did the LiveJournal blogging service, based in San Francisco.

Google’s Blogger site, which lets people create blogs, said a “small percentage of users” were affected by the attack today. No other Google sites were disrupted, the company said.

‘Minimize the Impact’

“Google has a variety of systems in place to help counteract these types of attacks, and we believe the majority of affected users can now access their blogs,” Blogger said. “We’re continuing to work to minimize the impact to affected Blogger users.”

Georgia and Russia fought a five-day war in August 2008 over the separatist region of South Ossetia. Russia said it sent troops into the region in response to Georgia’s “inhuman attack” on civilians and Russian peacekeepers. Georgia said Russian troops forced the country to launch a counteroffensive.

Russia beat the Georgian forces and later recognized South Ossetia and a second breakaway region, Abkhazia, as sovereign countries. Russia has thousands of troops in the regions, which Georgia considers to be occupied territories.

Facebook, the world’s most popular social-networking site, had 250 million users as of last month. No one had their personal data put at risk by the attack, the company said.

“We’ll keep monitoring the situation to make sure you have the reliable experience you expect from us,” Palo Alto, California-based Facebook said yesterday on its site.

Twitter had 20.1 million U.S. users in June, according to research firm ComScore Inc. in Reston, Virginia. That made it the third most popular social-networking site. News Corp.’s MySpace ranked second.

To contact the reporters on this story: Nikolaj Gammeltoft in New York at ngammeltoft@bloomberg.net; Rochelle Garner in San Francisco at rgarner4@bloomberg.net

Last Updated: August 7, 2009 18:48 EDT