Twitter, Facebook Sites Disrupted by Web Attack

Users were unable to access Twitter's Web site for about two hours starting around 9 a.m. EDT. Around the same time, Facebook users saw delays logging in or using the social network.

Facebook Inc. and Twitter Inc. were working together with Google Inc. to investigate what happened, according to a person familiar with the matter. Another person familiar with the attack said it may have been targeted at a single Russian activist blogger with accounts across the impacted services.

The companies traced the problem to what the computer industry calls "denial-of-service" attacks, which are designed to make sites inaccessible by overwhelming them with a flood of traffic. Though such attacks are fairly routine, simultaneous action against multiple consumer Internet companies is rare.

(...) Twitter said it was able to restore service, but said some users experienced "degraded" service while the company worked to recover completely.

Blogging site LiveJournal.com, which was also temporarily unavailable, said it was hit by a similar attack that began around 9 a.m. EDT. Soon afterward, Facebook disclosed that it experienced an apparent denial-of-service attack as well.