There were no tweets on the internet for close to three hours Thursday, due to a prolonged Twitter outage that has been blamed on a denial-of-service attack.

"As we recover, users will experience some longer load times and slowness," said the Twitter status blog shortly before 1 p.m. ET. "This includes timeouts to API (application programming interface) clients. We’re working to get back to 100 per cent as quickly as we can."

The social networking site's short-message service outage had started around 9 a.m. ET, reported the TechCrunch blog. Twitter's status blog first reported an outage due to an unknown cause around 10:50 a.m.

Within half an hour, the site confirmed that a denial-of-service attack was behind the outage. That type of attack prevents users from getting access to a network, typically by overloading the servers with a flood of useless traffic.

The traffic may be generated by a "bot net" of computers infected by malicious code that allows them to be harnessed together and remotely controlled.

Possible Russia-Georgia link

But one expert said the attack may be an extension of the conflict between Russia and Georgia.

The attack started with hackers using a botnet to send a flurry of spam email messages that contained links to pages on Twitter, Facebook and other sites written by a single pro-Abkhazia activist, according to Bill Woodcock, research director of the Packet Clearing House, a non-profit organization that monitors internet traffic. 

He said he had evidence that the attack originated in the disputed territory of Abkhazia.

When people clicked on the links, they were taken to the activist's legitimate web pages, but the process of loading the pages at such volumes overwhelmed some servers and disrupted service, Woodcock said.

He said it's hard to immediately tell whether it was a case of hackers trying to punish the sites for publishing views they disagree with, or if they were directing traffic to the sites out of sympathy for the activist's message.

"There's very little way of distinguishing which side was taking this action, because either side could hypothetically benefit from it," Woodcock said.

By 11:15 a.m., the Twitter status blog reported that the site was back up but "continuing to defend and recover from this attack." In the next hour, service remained spotty, and even Pingdom.com, which monitors uptime and downtime for websites, including Twitter, reported that the site was down at 11:30 a.m.

In total, the site was down for two hours and 50 minutes Thursday, Pingdom.com reported.

The Twitter outage began at about 9 a.m. EDT and lasted a few hours.

While long outages were common on the site two years ago, Pingdom's statistics show Thursday's outage is the longest in the past five months. During that period, the site was down an average of 82 minutes per month.

Facebook, whose users encountered intermittent problems Thursday morning, was also the subject of a denial-of-service attack, though it was not known whether the same hackers were involved, The Associated Press reported.

Unlike Twitter, Facebook never became completely inaccessible. Facebook said no user information was at risk.

With files from The Associated Press