Why is United Airlines suing a 22-year-old?

22-year-old Aktarer Zaman founded Skiplagged.com last year.

NEW YORK (CNNMoney)

United Airlines (UAL) and Orbitz (OWW) filed a civil lawsuit last month against 22-year-old Aktarer Zaman, who founded the website Skiplagged.com last year.

The site helps travelers find cheap flights by using a strategy called "hidden city" ticketing.

The idea is that you buy an airline ticket that has a layover at your actual destination. Say you want to fly from New York to San Francisco -- you actually book a flight from New York to Lake Tahoe with a layover in San Francisco and get off there, without bothering to take the last leg of the flight.

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This travel strategy only works if you book a one-way flight with no checked bags (they would have landed in Lake Tahoe).

It's not like these tickets are the cheapest all the time, but they often are.

In the lawsuit, United and Orbitz call Skiplagged "unfair competition" and allege that it is promoting "strictly prohibited" travel. They want to recoup $75,000 in lost revenue from Zaman.

Zaman said he knew a lawsuit was inevitable but he points out that there's nothing illegal about his web site.

He also said he has made no profit via the website and that all he's done is help travelers get the best prices by exposing an "inefficiency" in airline prices that insiders have known about for decades.

"[Hidden city ticketing] have been around for a while, it just hasn't been very accessible to consumers," Zaman told CNNMoney.

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Indeed, "hidden city," ticketing is no secret among frequent fliers, said Michael Boyd, President of Boyd Group International, an aviation consulting firm in Evergreen, Co. Boyd worked as an American Airline (AAL)ticket agent 30 years ago, and says he was trained at the airline to help customers find "hidden city" fares.

"I don't think it's illegal what he's doing," Boyd said. But lawsuits are expensive and it could end up costing the young entrepreneur who has irked the two billion dollar corporations.

Airlines usually offer cheaper fares for some destinations that are not regional hubs, Boyd said. Many of these flights are routed through more popular destinations. But if a lot of people take advantage of that discrepancy it could hurt the airlines, which is why they want to shut him down.

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Born in Bangladesh, Zaman grew up in Brooklyn, N.Y., and graduated with a bachelor's degree in computer science at age 20 from Rensselaer Polytechnic Institute. He lives in Manhattan and works at a technology start-up that he declined to name.

Zaman said Skiplagged is just a "side project."

Zaman and United declined to discuss the lawsuit. Orbitz said in a statement that it is obligated to uphold airline fare rules.

Other travel experts say that the airlines may not achieve much if Zaman's site is shut down, especially in a world where information is becoming more readily available.

"If [Skiplagged is] shut down, undoubtedly there will be other people to come along to scrape fares and make them available," said Robert Mann, president of R.W. Mann & Company, an airline consulting firm in Port Washington, N.Y.