NEW YORK (AFP) - United Airlines and online travel website Orbitz have filed suit against a young computer programmer who used a clever trick to get discounted airfares.

The lawsuit filed last month in Illinois federal court alleges that Mr Aktarer Zaman, who operates the website Skiplagged.com, illegally promoted use of the technique to get discounts.

Skiplagged, launched last year by the recent university graduate, enabled travellers to get a fare below the published rate by skipping the final leg of a flight.

The so-called "hidden city" fares provide tickets to a location that is not the final arrival destination, but an intermediate or connecting city.

The technique exploits a quirk in airfares - where some long-haul flights are less expensive than a short-haul journey.

For example, a customer buying a ticket from New York to Los Angeles, where competition is high, could get a lower rate than a flight to Chicago, but could simply get off the plane during a stop in Chicago and avoid a higher fare.

The lawsuit alleges that this technique represents "federal unfair competition, tortious interference with contract, breach of contract, and common law misappropriation."

The complaint maintains that "hidden city" ticketing "is strictly prohibited by most commercial airlines because of logistical and public safety concerns" and violates the terms of service of carriers.

Orbitz and United have asked the court to shut down Skiplagged and to award monetary damages.

Mr Zaman, who according to media reports is 22, posted a notice on his website that the lawsuit could "force us to remove results only we find, getting in the way of saving you lots of money on airfare."

He asked for contributions to his legal defense.

"I launched Skiplagged.com last year with the goal of helping consumers become savvy travellers," he wrote on the online forum Reddit, adding that the method "has potential to easily save consumers up to 80 per cent when compared with the cheapest on Kayak, for example. Finding these has always been difficult before Skiplagged because you'd have to guess the final destination when searching on any other site."

According to his LinkedIn page, Mr Zaman graduated last year from Rensselaer Institute of Technology and has worked as a software engineer for Amazon and Cisco.