The US Patent and Trademark Office (USPTO) has ordered the re-examination of a browser plug-in technology patent that has also been the subject of a legal battle between the patent's owners and Microsoft.

The re-examination order was issued on 30 October, according to the USPTO Web site. "Re-examintations of patents are fairly unusual," said Brigid Quinn, a USPTO spokeswoman. The patent will now go to the examiner's dock and will be handled like any other patent application."

The re-examination of patent number 5,838,906 (also knows as the 906 patent) could take anywhere from 12 to 18 months, Quinn said.

The move comes after the director of the World Wide Web Consortium (W3C), Tim Berners-Lee, sent a letter to US Under secretary of commerce for intellectual property James Rogan last month, urging the USPTO to invalidate the 906 patent due to the existence of "prior art," a legal term referring to technology in existence when a patent is applied for, when the patent was granted in November 1998.

The 906 patent was issued to the University of California Regents and is licensed exclusively to Eolas Technologies, whose president, Michael Doyle developed the technology at the University of California at San Francisco. The patent covers technology that allows interactive content to be embedded in a Web site, describing in part "a system allowing a user of a browser program... to access and execute an embedded program object."

In August, a Chicago jury ordered Microsoft to pay US$520.6 million in damages to Eolas Technologies and the University of California Regents, for the violation of the 906 patent. The Redmond, Washington, software company is appealing the ruling, but has also said it is making changes to Internet Explorer (IE), which the W3C contends may affect a large number of existing Web pages.

Due to its strong feelings, the W3C took the unusual step of becoming involved in the legal dispute and backing Microsoft. Berners-Lee and the W3C presented the USPTO with two prior art publications, "Raggett I" and "Raggett II," which the consortium said relate to HTML+, a proposed specification extending the features of HTML.

Representatives from the W3C, University of California Regents, Eolas Technologies and Microsoft could not immediately be reached for comment.