You could call it the sale of the century, but it's becoming a monthly occurrence. United Airlines, due to a website glitch, is selling plane tickets for nearly no cost.

One of our readers, who asked to remain anonymous, called the situation to our attention Monday afternoon, and gave us explicit instructions on how to exploit the glitch.

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We successfully tested the steps, but stopped one click short of purchasing the tickets — a roundtrip flight from Newark, N.J., to Dublin for $49.40, just the cost of taxes and fees.

Exploiting the glitch involved setting up a "MileagePlus" account and essentially tricking the site into thinking you had enough frequent flier miles to cover the cost of a flight by setting up the purchase in two different tabs. The entire process took less than 10 minutes and, at time of writing, was still functioning. United, however, declined to comment on how many people have tried to take advantage of the loophole.

United had a similar problem in September, though NBC News reported that the issue was due to "human error" on the airline company's part. United ultimately decided to honor the reduced-price tickets it sold because of that glitch.

That's not the case this time around, though.

"We’ve identified an issue where customers are intentionally manipulating our website," United spokesman Rahsaan Johnson told Mashable in an email. "We will not honor these reservations."

UPDATE: Oct. 14, 8 p.m. ET

United further clarified that the reason why it honored the reduced-price tickets mistakenly sold last month is because human error was the reason for that situation.

Image: David McNew/Getty Images