Chicago-based Eolas holds a license to the patent from the University of California and last year won a $521 million jury verdict against Microsoft in its patent infringement case. Microsoft has since appealed the verdict.
In an initial finding in February, a patent office examiner agreed that substantial "prior art" existed to reject the patents claims. Prior art is the legal term referring to whether an invention existed prior to the filing of a patent.
In its response, Eolas defended the patents validity and rejected the claims of prior art, said Eolas attorney Martin Lueck, of Robins, Kaplan, Miller & Ciresi LLP, in Minneapolis.
"We basically reiterated the arguments we set forth in the trial," Lueck said.
The patent, No. 5,838,906, was issued in 1998 and covers a method for the embedding and invoking of interactive applications, such as plug-ins and applets, in Web pages.
A patent office spokeswoman said the office had yet to receive the Eolas response, and neither Eolas nor University of California representatives would release a copy of the filing.
Following an examiners initial finding in a re-examination, the patent holder gets a chance to respond. The back-and-forth can continue, depending on the examiners next findings, and the entire re-examination process takes an average of 21 months, the patent office spokeswoman said.
Microsoft officials declined to comment on the filing, saying the company had yet to see it.