Security experts say the coordinated cyber attacks which temporarily shut down two popular social networking Web sites Thursday were aimed at silencing a Georgian blogger critical of Russian actions against his country.

Facebook's chief security officer Max Kelly said the simultaneous attacks were aimed at a user known as "Cyxymu" who had accounts on Facebook, Twitter, LiveJournal and other affected sites.

Media reports have identified "Cyxymu" as a 34-year-old Georgian economics professor named Georgiy.

In an interview with the Guardian newspaper, the blogger said he believed the attacks were an attempt to silence his criticism of Russia's conduct in the war over the breakaway region of South Ossetia, which began a year ago Friday.

Twitter co-founder Biz Stone said in a blog post Thursday that the company preferred not to speculate about the motivation behind the malicious attack.

Security experts said hackers appear to have hit "Cyxymu" with a two-pronged assault on Thursday.

They said the attackers first sent out a wave of spam which appeared to have come from "Cyxymu," a technique intended to discredit a user by making him appear to be the source of large amounts of junk email.

Then, the hackers launched a so-called distributed denial-of-service (DDOS) attack designed to overwhelm a website's servers with communications requests.

Georgiy, who has refused to give his surname in separate interviews with the media, says "Cyxymu" is the Russian spelling of his hometown, Sukhumi, the capital of Abkhazia, a second Georgian breakaway territory.

A large DDOS attack disabled a number of Georgian government Web sites during last year's conflict.

Some information for this report was provided by AFP, AP and Reuters.