The attack appears to be more of a nuisance than a threat to security.

US government websites have been reportedly knocked out by a widespread and unusually resilient computer attack that started Saturday. It is also said that the attack has knocked out even the websites of some agencies that are responsible for fighting cyber crime.

The Treasury Department, Secret Service, Federal Trade Commission and Transportation Department websites were all down at varying points over the holiday weekend and into this week, according to officials inside and outside the government. Some of the sites were still experiencing problems Tuesday evening, The Associated Press has learned.

However, US officials refused to publicly discuss details of the cyber attack.

The attack, while powerful, is not particularly sophisticated and appears to be more of a nuisance than a threat to security, according to It uses a variety of well-known distributed denial of service (DDoS) attacks that try to overwhelm websites with useless requests and make them unavailable for legitimate users, security experts say.

Suspected cyber attacks have also paralysed websites of major South Korean government agencies, banks and Internet sites including US Bancorp, the US Secret Service, the US Department of Homeland Security, the US Department of State, the White House, the US Department of Defense, the New York Stock Exchange, the Nasdaq and the Washington Post, according to security researchers studying the incident. The alleged attacks reportedly appeared to be linked to the knockout of service of websites of several government agencies in the US.