A new Internet virus nicknamed "Code Red" appears to be attacking websites worldwide, security experts said.
The worm defaces English-language websites hosted by the computers it infects, displaying the slogan "Hacked by Chinese!", they said. The origin of the virus was not clear.
The White House website is among those that have been hit by the virus.
The Code Red worm seems to instruct infected computers to launch a denial of service attack on the government website www.whitehouse.govof the kind that took down major Internet sites such as Yahoo! and eBay in February last year, analysts said.
The White House website, which is the home page for the Bush administration, was still accessible as of yesterday evening.
A denial-of-service attack is intended to render the target site inaccessible to legitimate traffic by swamping it with requests for information.
The Code Red worm could also slow overall Internet traffic by flooding the Web with message traffic from infected computers, said Mr Marc Maiffret of eEye Digital Security, a computer security company based inCalifornia.
Mr Maiffret estimated 12,000 computers around the world had been infected with the Code Red worm.