The Associated Press , New York, US | Fri, 08/07/2009 8:14 AM | World A hacker attack Thursday 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 toward a single site at the same time, preventing legitimate traffic from getting through. The attacks appear to have been related to the Russia-Georgia political conflict. They started with a flurry of spam e-mail messages sent out this morning that contained links to pages written by a single activist on multiple social networking sites, according to Bill Woodcock, research director of the San Francisco-based Packet Clearing House, a nonprofit that tracks Internet traffic. When people clicked on the links, they were taken to legitimate Web pages, but the traffic overwhelmed some servers and disrupted service, Woodcock said. He said i...