The US authorities are investigating a major cyber attack that knocked out the websites of several US government agencies in recent days. The attack began on July 4th and has affected websites belonging to the Treasury Department, the Secret Service, the Federal Trade Commission and the Transportation Department. Some of the sites were still experiencing problems earlier today, suggesting that the denial-of-service attack was extremely sophisticated. South Korea, meanwhile, says websites belonging to its government agencies and banks were also paralysed because of an identical attack.