The SCO Group said it is experiencing a distributed denial-of-service (DDOS) attack apparently related to the Mydoom worm that first appeared Monday.

The company, which is embroiled in legal action against IBM over intellectual property rights related to its ownership of System V Unix code, said it is offering a reward of up to US$250,000 "for information leading to the arrest and conviction of the individual or individuals responsible for creating the Mydoom virus."

In a statement, the company said it had been the target of several such DDOS attacks during the past 10 months: one in Decemberand one last August.

But the one now under way "is different and much more troubling, since it harms not just our company, but also damages the systems and productivity of a large number of other companies and organisations around the world," said SCO CEO Darl McBride.

"We do not know the origins or reasons for this attack, although we have our suspicions," said McBride, who did not elaborate on what those suspicions are. "This is criminal activity and it must be stopped."

The company also said it is working with US law enforcement authorities, including the US Secret Service and the FBI, to try to determine who might be involved in the attack.

The Mydoom worm, also known as Novarg and Mimail.R, is a mass-mailing worm that arrives via e-mail as an attachment with one of several possible file extensions, including .bat, .cmd, .exe, .pif, .scr or .zip. When a user opens the attachment, his computer becomes infected. The worm is apparently designed to attack the company's website, beginning on 1 February.

Experts have said that the Mydoom worm is spreading faster than last year's Sobig.F, which topped the charts as the most widespread e-mail worm of 2003.