Utah's SCO Group has asked a federal judge to declare that the general public license of the Linux computer operating system is unconstitutional and unenforceable.

The Lindon-based company made the motion as part of its request that U.S. District Judge Dale Kimball dismiss IBM's 3-month-old countersuit.

In its August countersuit, IBM denied SCO's allegations in its $50 billion March lawsuit that SCO's proprietary Unix code had been illegally incorporated into IBM's versions of the freely distributed Linux. IBM also accused SCO of breaking IBM patents, breach of contract, unfair competition, deceptive trade practices and violation of the Linux public development and distribution license.

In its response, SCO attacked the GPL.

"Apart from the patent issues, SCO views the GPL issues as much more significant," company spokesman Blake Stowell said Tuesday. "SCO's copyrights still stand. Congress has drawn a boundary between proprietary and open source."

IBM spokesman Mike Darcy would only say that his company "strongly believes in its counterclaims and looks forward to trying its case in the court of law."

However, open-source spokesman Bruce Perens, a Berkeley, Calif., Linux developer, blasted SCO's challenge to the GPL's constitutionality as being "way over the top."

Perens contended the enforceability of the GPL has withstood past court scrutiny, and he said SCO's filing was "just an attempt to delay the inevitable day that the case gets thrown out of court."

SCO argued that the chief enforcer of the GPL — the open-source community's Free Software Foundation — has been so selective and inconsistent as to render the license "barred as a matter of equity."

SCO contended that use of the license violates standing federal copyright, antitrust and export-control laws.

SCO, which is also being sued by leading Linux distributor Red Hat, filed its response late Friday.