The attack caused "some degradation" of service starting at about 8:00am eastern time, and blocked access entirely between about 9.00am and 11.15am, said spokesman Jimmy Orr, adding that technical staff are taking measures to bolster security at the White House servers.
It's not the first time hackers have targeted the US president's Web site. "It has happened during the past administration that the Web site was down for a day or two a few times," he said.
Asked whether investigators suspect a link between the incident and a series of recent attacks on US government servers attributed to Chinese hackers, Orr would only say, "I can't speculate at this time."
The US National Infrastructure Protection Center (NIPC), the office of the Federal Bureau of Investigation (FBI) responsible for computer security, warned late last month of an upswing in attacks against US servers by Chinese hackers, given the increasing political tensions between the two countries.
Contact the White House at http://www.whitehouse.gov .