The MyDoom worms have overloaded the SCO Group's website with a massive distributed denial of service (DDoS) attack.

SCO said that internet traffic began building momentum on 1 February, and by midnight its website was flooded with requests beyond its capacity.

The attack was programmed to start at 1609 GMT on 1 February but began earlier than expected due to incorrect clock settings on infected PCs. Hundreds of thousands of infected machines, including those of home users around the world, may be contributing to the onslaught.

"This large scale attack is now overwhelming the internet with requests to www.sco.com," said Jeff Carlon, worldwide director of IT infrastructure at SCO group, in a statement.

"While we expect this attack to continue throughout the next few weeks, we have a series of contingency plans to deal with this problem."

Some people believe SCO was targeted by the worm because of the comopnay's claim to own poarts of the open source operating system Linux.

MyDoomB, the first variant of the worm, is spreading, but not as fast as its predecessor. It is also scheduled to target Microsoft from midday (GMT) on 3 February.

Both SCO and Microsoft have put up a $250,000 bounty for information leading to the capture of the worm's creator.

"Obviously we do not discuss security measures, but we have been preparing for this," Stuart Okin, chief security officer for Microsoft UK, told Computeractive.

"We have researched the worm intensively and are watching for any activity against the website."

Both worms will stop the DDoS attacks on 1 March. Removal utilities are available from all major antivirus software vendors.