Data-networking firm Alacritech Inc., which has filed a patent-infringement suit against Microsoft Corp., was granted a preliminary injunction that could threaten the release of Longhorn, the software maker's next major Windows release.

A federal court in San Jose, Calif., last week issued the injunction that prevents Microsoft from "making, using, offering for sale, selling, importing or inducing others to use Microsoft's 'Chimney,' TCP offload architecture," Alacritech said in a statement. The technology, which is used to help networks run faster and more efficiently, is expected to be a part of Longhorn and in the Scalable Networking Pack for Windows Server 2003. Longhorn is set to ship in 2006.

Alacritech lawyer Mark Lauer said in a statement the injunction applied to only one of the "dozens of claims" pending in the case.

Alacritech declined further comment Thursday, "due to the ongoing nature of this litigation," company spokesman Joe Gervais said in a telephone message.

Microsoft denied that Chimney was based on Alacritech technology, saying it was "developed independently by Microsoft's own engineers."

"Microsoft, as an intellectual property company, invests heavily in research and development and is committed to respecting the IP rights of others," a spokeswoman said.

The suit alleges that Microsoft refused to license Alacritech's network-acceleration architecture covered in two patents. The technology is sold under the brand "SLIC Technology,"

In general, SLIC handles all of the network-protocol processing, which means more of a computer system's power can be used to keep up with high-speed data transmissions. The technology is used on networks based on TCP/IP, which is the protocol of the Internet.

Microsoft unveiled Chimney in the spring of 2003, and Alacritech offered the company a license a few months later, according to officials with San Jose-based Alacritech.

"Microsoft rejected licensing terms that would be acceptable to us," Larry Boucher, president and chief executive of Alacritech, said in a statement. "We were forced to sue Microsoft to stop them from continuing to infringe, and inducing others to infringe, on our intellectual property rights."

Alacritech sued Microsoft in August 2004.