NEW YORK: Hackers today shut down the fast-growing messaging service Twitter for hours, while Facebook experienced intermittent access problems.

Twitter said it suffered a denial-of-service attack, in which hackers command scores of computers towards a single site at the same time, preventing legitimate traffic from getting through.

The attacks may have been related to the ongoing political conflict between Russia and Georgia. They started with hackers using a botnet to send a flurry of spam e-mail 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 San Francisco-based Packet Clearing House, a non-profit organisation that tracks Internet traffic.

Russia recognised as independent the breakaway regions of South Ossetia and Abkhazia after a brief war with Georgia a year ago.

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.

The fact that a relatively common attack could disable such a well-known Web site shows just how young and vulnerable Twitter still is, even as it quickly becomes a household name used by celebrities, large corporations, small businesses and even protesters in Iran.

For Twitter users, the outage meant no tweeting about lunch plans, the weather or the fact that Twitter is down.

The Twitter outage began at about 9 a.m. EDT (1300 GMT) and lasted a few hours.

Facebook, whose users encountered intermittent problems on Thursday morning, was also the subject of a denial-of-service attack, though it was not known whether the same hackers were involved. Unlike Twitter, Facebook never became completely inaccessible. Facebook said no user information was at risk.