The number of re-examination requests has jumped sharply since about 2004, he said, in large part because of a court decision, in KSR v. Teleflex, that lowered the bar for showing that a technology was too obvious to be patented. Many of the requests have been filed by proprietary software companies.

Going to court over a patent typically costs US$1 million to $4 million, Lindberg said, while filing this type of re-examination request costs $50,000 to $100,000, depending on the complexity of the claim. That's still a tidy sum for a small company, but one that could be divided among several concerned parties.

Filing for a re-examination may be the only option for some companies, since some open-source licenses include a clause that revokes the license if the holder files a patent suit. A re-examination request can be filed anonymously in some cases, and it can be a handy bargaining chip for open-source companies that don't have patents of their own.

A request can be used in patent negotiations even if it is only prepared and not filed. "You can say to a company, license me your technology on fair and reasonable terms or I'll submit your patent for re-examination," Lindberg said. It is also less likely to aggravate the open-source community, which tends to frown on companies that litigate over patents.

Greg Olsen, who developed the open-source program SendMail and founded the company of the same name, said Lindberg makes a good point.