The distributed denial of service attack on Thursday that targeted Twitter, Facebook, LiveJournal, and several Google sites may have been politically motivated.
Citing Facebook Chief Security Officer Max Kelly, CNET reported that a Georgian blogger with accounts on Twitter, Facebook, LiveJournal and Google's Blogger and YouTube was targeted the attack.
Twitter was taken offline for more than two hours while Facebook's service was degraded, according to the companies.
Google said it had defended its sites and was now working with the other firms to investigate the attack.
Google systems prevented substantive impact to our services, the company said in a statement.
The search-engine giant did not confirmed which services were targeted in the attack, but it is thought that its e-mail service Gmail and and video site YouTube came under attack.
We are aware that a handful of non-Google sites were impacted by [an]... attack this morning, and are in contact with some affected companies to help investigate this attack, the company said.
Twitter co-founder Biz Stone wrote on its own blog: Twitter has been working closely with other companies and services affected by what appears to be a single, massively co-ordinated attack.