The Open Source Development Lab (OSDL) has challenged the legal basis for SCO's threat of litigation to Linux users.

The OSDL, now home to Linus Torvalds (pictured) and the Linux kernel, has published a position paper, entitled Questioning SCO: A Hard Look at Nebulous Claims, written by Professor Eben Moglen, an expert on copyright law.

In the paper, Moglen argues that SCO cannot license end users, and identifies key questions for companies to ask SCO.

Moglen said: "[SCO's] failure to come forward with evidence of any infringement of SCO's legal rights is suspicious in itself.

"SCO's public announcement of a decision to pursue users, rather than the authors or distributors of allegedly infringing software, only increases doubts."

Key questions which Moglen says users are entitled to ask include:

The professor contends that, by having itself distributed the Linux kernel, SCO cannot claim that a trade secret is being made public or that it took reasonable measures to maintain secrecy.

SCO has not alleged breach of patent or trademark leaving it only with copyright claims, and these cannot apply to end users, he said.

The position paper makes three main points:

Moglen is a faculty member at Columbia University Law School and has been a general counsel for the Free Software Foundation for 10 years.

The paper is based on a presentation he gave to the first meeting of the OSDL customer advisory council a week ago.

SCO could not be reached for comment at time of going to press.