HELSINKI, Feb 1: A fast-spreading e-mail worm targeting US software manufacturer SCO is gaining ground as more and more computer users switch on infected machines, while experts say a major Mydoom attack on SCO is timed to hit at 1609 GMT.

"It seems that the attack is showing its first effects... Yesterday I was able to connect to the SCO site, today it's impossible," Mikko Hyppoenen, of the Finnish anti-virus firm F-Secure said.

Some experts say the Mydoom worm may be the work of pro-Linux activists, which are angry at SCO's effort at copyrighting parts of the free operating system.

F-Secure, a leading provider of security for companies' computer systems, including anti-virus software, has described Mydoom as the "fastest spreading e-mail worm in history."

Mydoom has left hundreds of thousands of computers vulnerable to hackers, spammers and other cyberspace outlaws, and its economic fallout has been estimated at 26.1 billion dollars (21 billion euros) so far, according to the British security firm mi2g.

Mydoom arrives as an e-mail attachment that sends itself out to other e-mail addresses if opened, and may allow unauthorised access to computers.

Mydoom. A, the original version of the Mydoom worm first detected on January 26, is programmed to attack the SCO website at 1609 GMT Sunday, most likely forcing it to crash.

F-Secure's Hyppoenen said the consequences for SCO would not be as dramatic as for companies that rely solely on their websites to conduct their business.

"It's not the end of the world (for SCO) like it would be for Amazom.com, for instance," he said, referring to the Internet retail leader. -AFP