A reservation tip that could save hundreds of flights has been used for years by savvy travelers. But someone has just been broken, news.com.au news.

The hack of the "hidden city" has always been one of the best kept secrets of flyers.

It is strategically giving up the liaison of a flight to avoid the higher cost of non-stop flights.

It's a sneaky but effective trick, and even though the airlines have long disapproved of it, savvy travelers have been using it for years to save money.

But right now, one of the world's largest airlines is looking to sue a passenger for doing it.

The German airline Lufthansa asks to be paid by a passenger accused of deliberately buying a plane ticket without intention to fly over the road.

According to The Independent, a first trial was rendered in favor of the passenger, but Lufthansa has now been allowed to appeal.

HANG ON, WHAT IS THE CACHE OF THE HIDDEN CITY?

Suppose you want to travel from London to Hamburg, Germany.

At present, you can get a direct flight from both cities for around $ 147, according to the Skiplagged booking website.

Skiplagged: The website promises to help passengers "find flights that airlines do not want you to see." Skiplagged: The website promises to help passengers "find flights that airlines do not want you to see."

You can also book a flight London-Cologne with a stopover in Hamburg for $ 109 and not embark for the return leg in Cologne, because Hamburg was actually your final destination.

You have traveled the same distance for a lot less money. And the longer flights are, the greater the potential savings.

SO, DO THE AIR COMPANIES KNOW?

Passengers will pay airlines more for non-stop flights, which is why these flights may cost more than a stopover flight over a longer distance. When you have a headache dealing with an AWOL passenger, including delays, it's no wonder airlines do not like this hack.

It seems that Lufthansa is the example of a passenger to dissuade others. The Independent pointed out that it was quite rare for passengers to be challenged or forced to pay the difference.

However, airline transport conditions warn passengers of the city's hidden piracy.

Lufthansa appears to be cracking down on a passenger accused of using the city's hidden trick. Photo / Getty Images Lufthansa appears to be cracking down on a passenger accused of using the city's hidden trick. Photo / Getty Images

Qatar Airways, for example, wrote: "If you change your transport without our agreement or if you do not follow the full booked itinerary, we will evaluate the correct price for your actual trip.

"You will be required to pay any difference between the price paid and the applicable total price, as well as any applicable administration fees, for your revised transportation."

Most airlines have a similar disclaimer in similar language.

WHAT ARE THE OTHER RISKS OF HACK?

Piracy in hidden cities has become a reliable way to save money on flights. Websites like Skiplagged have appeared to help passengers compare their options. (United Airlines sued Skiplagged in 2015 but was not able to close the site.)

First, the passengers must be confident when they finish their trip in the city of call, they can pick up their luggage at the airport.

Checked baggage is often tagged to the final destination, which means that even if you finish the trip, your luggage may not be. Veteran hackers often travel with only cabin bags to avoid this problem.

Passengers must also know if they are showing up. The airline will cancel all other flights listed on their reservation.

Another mistake made by novice pirates is to skip the first leg of the trip, as opposed to the last one. The entire trip will be canceled if you do not show up for the first flight.

And there is no point in trying cheap airlines because they charge their flights segment by segment, according to The Independent.