Nathan Bruckner visits a friend in Montreal every year. But he says airfares in the summer have gotten out of hand, costing close to $600 for a non-stop, round trip ticket. 

"It's the difference between doing the trip or not right? because it's a short trip, you know it's not a must have," Bruckner said.

Then the Manhattan resident discovered Skiplagged, a controversial website to search for so-called "hidden-city" fares. 

Skiplagged finds instances when a ticket to fly from city A to B to C is less expensive than a ticket from A to B. Instead of traveling to the final stop, the traveler departs at the midway point.

For example, we found a direct flight from New York to City to Cleveland for $443.

The cheapest Hidden City Ticket? $280 by booking a trip to Chicago with a stop in Cleveland, and getting out there. About 25 percent of searches find savings.

Aktarer Zaman, who was born in Bangladesh, emigrated to Brooklyn, and graduated from Brooklyn Tech High School invented the "Skiplagged" search engine five years ago after stumbling upon hidden city fares. 

He discovered a ticket from New York to San Francisco cost hundreds of dollars more than a ticket from New York to Seattle with a layover in San Francisco. 

"I was just wondering how big is this?" Zaman said.

It's big enough that United Airlines took him to federal court. A judge threw out the lawsuit but the National Association of Airline Passengers warns the fine print on most airplane tickets typically forbids hidden city fares. 

"And they can come back after you for damages. And in some cases the airlines have revoked frequent flier status and canceled their miles and things of this sort," explained Douglas Kidd, Executive Director of the National Association of Airline Passengers.

Zaman defends hidden city ticketing saying consumers have the right to decide how much or how little to use what they're buying.

Well more than a million people agree, booking flights through skiplagged despite the risks, and inconvenience. You cannot check a bag if you're ending the trip at the layover city or it will end up at the wrong destination.

Zaman also advises customers to only use the service a couple of times a year to avoid drawing attention to themselves.

"The people who are at risk are using it 10, 20 times a year," Zaman said. 

Passenger advocates say sites like Skiplagged could force the airlines to change their pricing models, basing them more on distance and less on demand.

It's quite an impact, for an immigrant from Brooklyn, and the website he built.