The new patent could spell trouble for dozens of e-commerce sites that use similar technology to recommend books, videos or other products to customers, patent experts say.
"There are a lot of services like that which would fall within the class of parties that could be sued under this patent," said Daniel Harris, an intellectual property attorney in Palo Alto, Calif., with Brobeck Phleger & Harrison.
Amazon spokeswoman Patty Smith declined to say whether the company would enforce the patent but said Amazon's "track record" should be looked at.
"We've defended one patent against one competitor who had a track record of copying features from our site," Smith said.
But it is precisely Amazon's track record that has many in the Internet community concerned. The recommendation service patent is the latest of six issued to the e-commerce giant.
The company's patent on its 1-Click purchasing technology led to a lawsuit against rival Barnesandnoble.com, which Amazon accused of illegally copying the system.
A later patent on its affiliates program led to criticism that Amazon's patents would harm e-commerce and the Internet because it covered obvious and widespread technology. Similar charges have been leveled against Priceline.com, which is embroiled in a patent dispute with Microsoft spinoff Expedia.com.
Amazon chief executive Jeff Bezos responded to the criticism by calling for patent reform. The U.S. Patent and Trademark Office has said it will give greater scrutiny to online business and e-commerce patents.
Amazon's recommendation service patent, issued earlier this month, covers the company's defunct BookMatcher service, a type of collaborative filtering technology. Through BookMatcher, an Amazon customer rated books that he or she read. The service then provided that customer with recommendations on other books based on the ratings of customers with similar tastes.
BookMatcher has since evolved into Amazon's present recommendation service, Smith said. The service does not require customers to rate books or other items beforehand; instead, it bases recommendations in large part on customers' purchases.
Amazon used the patented technology to jumpstart its recommendation service, Smith said. She declined to say whether the company would pursue a new patent on its updated service.