It could blow up in BT's face and if it doesn't it will have far-reaching effects for the whole internet industry

Ben Goodger, lawyer

A hyperlink is the highlighted - often underlined - text on a website that lets you click from one site to another.

BT is determined to prove that a patent lodged with the US patent office back in 1980, when the World Wide Web was just a twinkle in Tim Berners-Lee's eye and BT was part of the Post Office, is still valid.

Old technology

The company claims that every US hyperlink is its intellectual property and therefore subject to a licensing fee. If successful, every internet service provider in the US would be liable to pay BT for the use of the technology.

The UK patent has already expired so ISPs in the UK would escape having to pay anything. But in the US, the patent does not expire until 2006.

The original patent was part of a technology called Prestel - an early system of linked computers that the Post Office was developing.

BT stumbled upon the patent during a routine update of its 15,000 global patents in the summer of 2000.

Language of patent

On Monday, a judge will look at the definitions of the patent in readiness for a full trial to take place later in the year.

Prodigy, owned by the US's second largest telephone company SBC, argues that the language used in the patent is too vague to apply to hyperlink technology as we know it today.

BT disputes this.

"In the original patent we use the term 'remote terminal means' which nowadays means PCs," a BT spokeswoman says.

"Prodigy is asserting that remote terminals cannot be construed as PCs," she adds.

Technology lawyer with Willoughby and Partners Ben Goodger believes the case could hinge on the language of the patent.

"The terms of the patent cover the technology they had in mind at the time. The question is whether the words are sufficiently precise to cover the technology used in the internet," he says.

Patently ludicrous

However, according to the UK Patent Office, patents are, by nature, vague so such an argument might not prove to be sufficient defence.

Part of BT's patent (see internet links)

"If I patented a flying machine the patent could equally apply to helicopters and aeroplanes even though they are completely different," explains Stephen Probert deputy director of the Patent Office.

"It seems ludicrous that a patent for one technology can cover another but patents are anything but precise and are meant to cover things that aren't yet invented," he says.

Video evidence

A stronger case could be made if the defence could prove the patent was invalid because the invention was not original. Here Prodigy has a killer piece of evidence up its sleeve.

Prodigy's unlikely saviour comes in the form of a fuzzy black and white video which shows a 1968 demonstration by Stanford computer researcher Douglas Engelbart apparently demonstrating hypertext linking.

Engelbart has an impeccable internet pedigree being the second person to link up to the US defence department's ARPANet, widely regarded as the forerunner to the modern internet.

Whether the film will be enough to sink BT's claim is of course not known, and some argue BT would not have taken the case to court if it was not convinced it could win.

Whichever way it goes, the case will one of the most exciting for years thinks Mr Goodger.

"It could blow up in BT's face and if it doesn't it will have far-reaching effects for the whole internet industry," he says.

The case could also be a public relations disaster for a company not always seen as the best friend of the internet. Its slowness to adopt unmetered internet access and broadband have come in for huge criticism at home, and it's reputation across the pond could be equally damaged by this court claim.

New chairman Sir Christopher Bland remains defiant. At the announcement of its quarterly financial results Sir Christopher claimed it was not in the business of making friends with US ISPs.

BT chairman is not worried about public relations

"The idea that we should abandon the suit for the feel-good factor for ISPs is bizarre," he said.

On the outcome of the case, he was more reticent. "If the court decides in our favour then that will be nice. If it doesn't that won't be so nice."

A sentiment, if reversed, that US ISPs would undoubtedly agree with.

See "internet links" for the text of BT's patent. There is no charge for doing so.