If you've got a website, you could owe this company millions...

Every website that uses a common form of site navigation could be hit for thousands or even millions of dollars in licence fees, if a US company which claims to hold a patent on the idea gets its way.

SBC Communications, a major American telco and ISP, says that it owns the right to links that stay visible on the page during navigation - and wants up to five per cent of company revenue annually as a licence fee.

In an email sent to the site www.museumtour.com, SBC said: "Your site includes several selectors or tabs that... seem to reside in their own frame or part of the user interface. [These] appear to infringe several issued claims in our patent."

The company also included a schedule of fees, which show that the 'base rate' for licensing for a company with a $100,000 (£62,000) turnover is $5,270 (£3,300) a year, rising to $16m for a $10bn company.

Web application developer DJ Walker-Morgan said: "What they are patenting is the entire process of structuring documents for the web, something that has been done since the advent of the web in the early nineties. They must know that they have a vague and challengeable patent; what other reason would they go after small companies like museumtours, and not after Amazon, AOL or Microsoft?"

The US patent in question, number 5,933,841 titled "Structured Document Browser", was issued in 1999 and hasn't been tested in court. It is part of patent law that 'prior art', where the patented idea was previously published, can invalidate a patent. However, ascertaining the validity of a patent is a costly and lengthy affair, and if it holds then SBC stands to claim licence fees from virtually every company in the US that puts links in frames on their websites.

The last major patent attack on the web was by BT, which claimed a year ago that it held the intellectual rights to hyperlinks and was thus due substantial licence fees. That went to court but was swiftly thrown out, in part because it pre-dated the web and thus talked of 'pressing selected keys on a keyboard' to activate links, whereas users these days use mice.