An executive at social networking site Facebook says hacker attacks that disrupted the service were aimed at a single blogger rather than the entire site.
Facebook and micro-blogging site Twitter were disrupted by the cyber attacks on Thursday. Twitter was down for more than two hours before engineers at the California firm were able to get it back online.
The Facebook executive said the cyber attacks were aimed at a Georgian blogger with accounts at the various affected sites, according to a report on technology news site CNET.
The blogger, known as Cyxymu, has told the BBC he blames Russia for the assault, though the broadcaster reports security researchers as saying there is no suggestion the attack was state-endorsed.
The BBC reports a botnet, or network of computers under the control of hackers, was directed to request the blogger's pages at such a rate that it slowed services for other users, in a denial-of-service attack.
Members of Facebook, the world's largest Internet social network with more than 250 million active users, saw delays logging in and posting to their online profiles.
The attacks came a month after the White House website was targeted in a similar online assault, underscoring the vulnerability of fast-growing internet social networking sites that have been heralded as powerful new political tools to counter censorship and authoritarianism.
Twitter, which allows people to broadcast short, 140-character text messages over the Internet, became a key form of communication in Iran amid the protests and clampdown that followed the country's disputed June elections.
Motives for denial-of-service attacks range from political to rabble-rousing to extortion, with criminal groups increasingly threatening to hobble popular websites that don't pay demanded fees, according to security experts.
In July a wave of similar attacks disrupted access to several high-profile US and South Korean websites, including the White House site. South Korea's spy agency said at the time that North Korea might have been behind the attacks.