Two of the four companies that SCO has publicly named as having bought a licence from it to use Linux, have denied doing anything of the sort.

Both Computer Associates and Leggett & Platt have been held up by SCO as purchasing a $699 (£384) licence to cover the alleged SCO copyrights in the open-source operating system. But both have publicly stated that they have done no such thing.

The chief architect of CA's Linux Technology Group, Sam Greenblatt, admitted the company had struck a deal with an investor in SCO over UnixWare licences and said that for each UnixWare licence bought, it was indemnified against a Linux box but he denied outright that the company had bought a licence specifically dealing with Linux.

Leggett & Platt was even clearer. "I have now talked to our people who handle our Linux systems and, at least at a corporate level, we have not bought such a licence from SCO Group," said the company's VP of human resources, John Hale. "To their knowledge they would not have an interest in doing so."

The denials come the same day that SCO was forced to admit an email appearing to demonstrate that Microsoft had helped fund the group to the tune of $86 million was real. But, the company claims, the email does not show what people claim it does.

This same misunderstanding approach was used by SCO to explain CA's statement. SCO spokesman Blake Stowell said that CA had indeed obtained an IP licence for Linux in an email. “UnixWare licences allow SCO customers to run UnixWare and the SCO Intellectual Property Licence allows Linux end users to run our Unix intellectual property in binary form in Linux. Today, CA has a licence in place to run our Unix IP in binary form in Linux without fear that they may be infringing on our intellectual property."

This hazy distinction angered CA's Greenblatt, who strongly objected to the portrayal of CA as a IP licensee for Linux. "To represent us as having supported the SCO thing is totally wrong," he said, before accusing the company's tactics as "intended to intimidate and threaten customers". "We totally disagree with [Darl McBride's, SCO CEO] approach, his tactics and the way he's going about this," Greenblatt added.

SCO claims to have copyrighted material within the Linux open-source operating system and has embarked on a dramatic legal battle to enforce them. Earlier this week, it expanded its lawsuits to include one of its own customers and a company using the Linux software and warned that it "will take and continue to take" legal action against Linux end users. The company sees itself as educating people about its rights in the same way that the RIAA - the US music industry body - has sued individuals in an attempt to prevent the free trade in copyrighted music.

However, one financial analyst said that the conditions surrounding the CA licence did not cast a favorable light on SCO. "I think it just speaks to the weakness of their case. Why could CA have not been convinced to take a licence without legal action," said Dion Cornett, managing director with Decatur Jones Equity Partners.

The other two companies that have been named as IP Licence for Linux customers are EV1 Servers.Net and Salt Questar. Both have confirmed that they did purchase SCO's licence.