White House website available despite attack
The virus, called Code Red, has already infected around 200,000 computer systems around the world, defacing many websites with the message "Hacked By Chinese".
The infected systems were scheduled to bombard the numerical internet address that represents the White House website on Thursday.
But security experts said officials apparently moved the site to a different address, dodging the internet bullet.
"We have taken preventative measures aimed at minimising the impact of any computer virus," said a White House spokesman, without going into details.
'Significant threat'
The Code Red worm works as a denial of service attack, designed to hamper or shut down a computer system by flooding it with huge amounts of data.
The FBI's National Infrastructure Protection Center has issued a warning, describing the virus as a significant threat that could "degrade services running on the internet".
Infected systems are likely to see their network performance degraded as a result of the scanning activity of the worm, warned the Computer Emergency Response Team (Cert).
Experts said the Code Red worm could slow overall internet traffic by flooding the web with message traffic from infected computers, putting the estimated number of infected systems at about 200,000.
Server security hole
Worms are programs that have the ability to spread across the web and execute instructions.
The Code Red worm exploits a vulnerability in Microsoft Internet Information Server 4.0 and 5.0 and affects computers running Windows NT 4.0 and Windows 2000.
The flaw was first identified in June and Microsoft released a patch that would prevent a computer from being infected with the worm
But it appears many administrators have not plugged the security hole. Even Microsoft failed to completely protect its network, admitting that a small number of servers were infected.
The worm seems to deface only English-language servers. It selects 100 IP addresses, scanning the computers associated with them for the security hole and spreading it to vulnerable machines.
Second worm
The worm then defaces websites hosted by the servers with the text: "Welcome to http://www.worm.com! Hacked by the Chinese!"
The origin of the virus is not clear. A second worm was discovered this week, called W32.Sircam.
It sends copies of itself to all email addresses in an infected computer's address book and can delete files and directories, fill up the hard disk and send files out to the internet.
Both English and Spanish-language versions have been found in more than 50 corporate networks worldwide, said Network Associates.