The SCO Group Inc.'s website has been knocked out of service by a denial of service (DoS) attack, the company confirmed on Wednesday.

The attack began at 11:20 am GMT on Wednesday, shutting down the company's main www.sco.com website, according to company spokesman Blake Stowell. He added that the company was working on restoring service.

Wednesday's attack was caused by a distributed "syn attack" that involved thousands of servers, which overloaded SCO's website, the company said in a statement.

In addition to the www.sco.com and www.caldera.com websites, the company's e-mail, intranet and customer support operations were also affected, SCO said.

SCO has raised the ire of the open source community by claiming that the Linux operating system contains software that violates SCO's intellectual property. The company has warned Linux users not to run the operating system without first purchasing a licence from SCO, and is on the verge of suing a major Linux user, according to Stowell.

The company's website was hit by a DoS attack in May, two months after it launched a lawsuit against IBM for allegedly misappropriating SCO's Unix source code and contributing it to Linux. A second DoS attack occurred in August, when SCO's site was disabled for a number of days.

The August attack was perpetrated by a "senior" member of the open source community, according to open source advocate Eric Raymond.

Raymond condemned Wednesday's attack. "The open-source community has condemned crack attacks on SCO in the past, and I don't believe any of our people are involved in this alleged attack," he said by e-mail. "No point to it; SCO's case is sinking fast."

SCO does not know the identity of Wednesday's attacker or why the attack was launched, Stowell said.