New York (NY) - The U.S. Patent and Trademark Office has agreed to re-examine Microsofts controversial FAT patent by request of the Public Patent Foundation (Pubpat). Microsoft is confident that the government afgency will confirm the validity of its patent.

In response to a request from April, the Patent Office said Friday that it will revisit patent 5,579,517, described as "Common name space for long and short file names." According to Pubpat, the agency said that it has raised "a substantial new question of patentability" regarding every claim of the patent.

Microsoft now has the opportunity to make an opening statement to the Patent Office, to which PUBPAT has the right to make a response. After opening statements, if any, the Patent Office will proceed to determine whether the patent is indeed invalid in light of the new questions raised by Pubpat's request. Third party requests for reexamination are successful in having the subject patent either narrowed or completely revoked roughly 70% of the time, Pubpat said.

"The USPTO often grants re-examination requests, and they provide an important mechanism to assure high levels of patent quality," answered David Kaefer, director of Microsoft's intellectual property and licensing group, in a statement.

"We are obviously very pleased with the Patent Office's decision to grant our request to reexamine Microsoft's FAT patent," said Dan Ravicher, Pubpat's Executive Director and Founder. "This is the first step towards ending the harm being caused to the public by this patent that should have never been issued."

The FAT file system has received growing attention in the light of its use not only with computers, Samba and Linux systems but especially with Flash memory cards. In December 2003, Microsoft announced that it would begin charging license fees for the use of the technology: The licensing model outlines $0.25 per unit or a maximum one time charge of $250,000.