A London-based IP company is suing Amazon and BarnesAndNoble.com for allegedly infringing on its Web-tracking patents.

BTG has filed suit in the States and alleges that the companies use BTG's patented technology as part of their online marketing programs. It asks for unspecified damages for past infringement and injunctions against future use of the technology.

BTG argues that Amazon, Barnesandnoble.com, online movie rental service Netflix, and shopping site Overstock.com have infringed US patent 5,717,860, titled "Method and apparatus for tracking the navigation path of a user on the world wide web".

It also alleges that Amazon and Barnesandnoble.com infringed its US patent 5,712,979, "Method and apparatus for attaching navigational history information to universal resource locator links on a world wide web page". Both patents relate to technology that enables the tracking of users between Web sites and were acquired by BTG from personalised Web information provider Infonautics in 2002.

BTG spokesman Andy Burrows said that the company researched the patents before purchasing them and was aware that the technology was used by a number of companies. It made efforts to persuade the companies to license or buy the technology before it filed suit, he said. "Litigation is part and parcel of doing business in the IP technology spectrum," Burrows said. He added, however, that "the floor was still open to reach commercial settlement."

The complaint against the four companies was filed on Tuesday but BTG has not yet heard from the defendants, Burrows said.

A spokeswoman for Amazon in the UK said that the company does not comment on pending litigation. Representatives for Barnesandnoble.com, Netflix and Overstock.com, all based in the US, weren't immediately available to comment.

Earlier this year BTG filed suit against Microsoft and Apple for a patent related to Web-enabled software update technologies. Although the company is prepared to engage in litigation, BTG gets the majority of its income from licensing and royalty revenue, Burrows said. BTG holds some 3,500 patents in its portfolio and brought in revenue of around £50 million in the last year.

Gary Barnett, IT research director at consulting company Ovum, said that he has noticed an increasein IP lawsuits in the tech sector recently. "They have become more important because people have run out of new ideas and they have started looking at old ideas and how to exploit them," Barnett said. He added that there are fewer suits in periods of sector expansion and innovation.

Patent lawsuits are can prove lucrative, however. Earlier this year chipmaker Intel agreed to pay Intergraph $225 million to settle a patent suit over a parallel instruction computing technology. And last year, eBay was ordered to pay $35 million for infringing a patent related to online auctions.

Although Burrows declined to say how much money BTG is seeking in its latest patent suit, he said that the value of the patents were "significant" to the company's operations.