A patent recently obtained by Microsoft for its Palm-sized PC product line is raising concerns among intellectual property experts who say it could be used to demand licensing fees from other mobile-device makers.

The patent, issued by the U.S. Patent and Trademark Office on April 27, covers what Microsoft calls a "time-based hardware button for application launch." Microsoft said the technology was developed for use in handheld computers, such as its Palm-size PC, which use buttons to open files and start programs.

In its patent application, Microsoft said the purpose of the now-patented technology is to make it easier for users to launch applications by either double-clicking a button or holding one down.

But the wording of the patent is drawing fire from some critics of the patent office, who view it as another example of how companies are obtaining patents that are either overly broad or apply to technologies already widely in use.

"What was the patent office thinking?" wondered Brandon Shalton, founder of Fight the Patent, a site that protests questionable patents. "I'm just kind of amazed that this patent was filed so late and was approved. It's a double-click. It was novel and unique 10 to 15 years ago."

Microsoft filed for the patent in July of 2002, but its application includes content from an earlier filing, made in 1999, which was subsequently abandoned.

In an e-mail, a Microsoft spokesman said the company would consider seeking licensing payments from those who employ technologies covered in the patent. But, he declined to reveal who the company might target, saying, "Microsoft receives dozens of patents every week. We don’t speculate on what products may or may not infringe patents."

If Microsoft does decide to sue for infringement, its lawyers should have a hard time proving their case due to some vague terminology used in the patent, said Dan Ravicher, executive director of the Public Patent Foundation.

One stumbling block, Ravicher said, is that the patent applies only to application buttons used in a "limited resource computing device." Because no definition of "limited resource computing device" is included, it's unclear what kinds of gadgets would fit that category.

Still, Frank Bernstein, a partner at the law firm Sughrue Mion, said an initial reading of the patent indicated that examiners investigated Microsoft's claim thoroughly before it was approved, looking at examples of prior technologies, such as the Palm III handheld.

"My visceral reaction is this is not a patent I would characterize as frivolously obtained or frivolously granted," Bernstein said.

Bernstein said it's quite common for a patent to appear, at first glance, as if it refers to technologies that have been in use for many years. The Microsoft patent, with its references to practices like double-clicking and holding a button down, is no exception.

However, he added, it's important to note that the patent only applies to the use of double-clicking or extended button-pressing in a particular context, with a particular type of device and for a particular purpose.

Moreover, Bernstein said, it's possible that Microsoft will never attempt to enforce its patent. Instead, the company may merely use the patent defensively to ward off suits from holders of similar intellectual property claims.

Of course, Bernstein could also envision the software company taking a different approach.

"If Microsoft were to become more aggressive in its Pocket PC business, I could see them asserting this patent offensively," he said.