Around a dozen US government websites, including those of the White House and the Pentagon, have been targeted in a coordinated cyber attack.

The Department of Homeland Security confirmed that the US government and the private sector's websites had come under the so-called "distributed denial of service" (DDoS) attack but declined to identify any of the targeted sites.

A denial of service attack attempts to paralyze a website by flooding it with traffic from an army of malware-infected computers known as a "botnet."

"It was a pretty massive attack," Johannes Ullrich, Chief Technology Officer for the private SANS Internet Storm Center, said of the Internet assault which began over the weekend.

Ullrich said US government sites which came under attack included the White House, Department of Homeland Security, Department of Transportation, Federal Aviation Administration, National Security Agency, State Department, US Postal Service, US Treasury Department and Voice of America.

A Pentagon site, defenselink.mil, was also targeted, he said, as was a site for US forces in South Korea.

South Korea's intelligence service believes North Korea or its sympathizers may have staged the attack.

The Department of Homeland Security confirmed the attacks but stressed that cyber attacks on US government websites were a daily occurrence and declined to identify any specific targeted sites.

SG/SME/RE