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NEW YORK — He was a whiz kid up against a $21 billion company.

Aktarer Zaman, now 23, didn’t back down when United Airlines and Orbitz sued him a little over a year ago for opening a website called to help travelers find cheap plane tickets.

Zaman says his site is now flying high and he’s often working seven days a week to keep up with demand.

“It’s been a fun journey. Looking back it’s been a very interesting experience that most people don’t get to experience,” Zaman told CNNMoney.

United and Orbitz were livid about Skiplagged, calling the start up website “unfair competition” that promoted “strictly prohibited” travel. They filed a federal lawsuit and demanded Zaman pay them $75,000 in lost revenue.

“I was not optimistic that I could take on the legal fight,” Zaman said. “I was a little afraid. I wasn’t sure what to do.”

But Zaman also got his back up. “Some people might just give in. I challenge that sort of thing. I’m really persistent,” he said.

Skiplagged helps travelers find cheap tickets through 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 book a flight from New York to Portland with a layover in San Francisco and get off there, without bothering to take the last leg of the flight. Sometimes, that can save you money. Flying this way isn’t always cheapest, but it often is.

Facing two corporations worth billions, Zaman asked for help and got it. Shortly after CNNMoney reported on the case, Zaman received a flood of donations on his GoFundMe campaign.

Zaman — who started Skiplagged while working at a tech startup — asked for $10,000 to help pay for legal fees and lawyers. Donors gave him $81,000.

In February, Orbitz backed out of the case and settled with Zaman, but United kept pursuing it. In May, a judge in Chicago dismissed the case because Skiplagged wasn’t in his jurisdiction. United didn’t pursue further legal action.

Zaman took a victory lap on Skiplagged, where the homepage touts the site’s success: “We’re so good, United Airlines actually sued us for it.”

Zaman’s life has changed a lot from a year ago. He’s been interviewed on national TV, hailed across social media and seen a surge in business.

And he’s not a one-man show anymore: He hired two full-time engineers, rented office space in Manhattan and received funding from angel investors (he won’t say how much or from who). He wants to hire more engineers.

A year ago, Skiplagged received about 250,000 visitors a month. Now it’s getting 1 million visitors a month on average. Skiplagged is one of the most popular travel apps in Apple’s store.

In late November, Zaman, did a Q&A on Reddit. It’s already among the top 10 Reddit Q&As ever, more popular than presidential candidate Bernie Sanders an hacker Edward Snowden and just below Tesla CEO Elon Musk.

He has cash left over from the legal donations. Zaman said he plans to donate $23,000 to a charity related to travel early next year.

So what gave him confidence to fight a corporation?

Zaman says he and his lawyers realized early on that United’s case was flawed. United claimed Zaman broke the “contract of carriage,” but that’s a contract between passengers and airlines — not third parties like Skiplagged.

United sued Zaman in a court in Illinois, where it is based. Skiplagged is in New York. Ultimately, that technicality helped get the case thrown out.

Zaman said he makes no profit on Skiplagged, but he doesn’t want to sell it or work at big tech company. He just wants to lift the curtain on a little known secret among frequent fliers.

“I’m just providing people with information and making them more informed,” he said. “I never saw that as a bad thing, making people be more skilled travelers.”