Website Mashable said a reader alerted the site Monday to a loophole on the airline's website that allowed customers to purchase tickets for only the cost of taxes and fees by setting up a "MilagePlus" account and tricking the site into thinking frequent flier miles were available by setting up the purchase in two tabs.
Mashable said the glitch resulted in a roundtrip ticket from Newark, N.J., to Dublin, Ireland, showing a cost of only $49.40.
"We've identified an issue where customers are intentionally manipulating our website," United spokesman Rahsaan Johnson said. "We will not honor these reservations."
United previously had numerous tickets sold at steep discounts last month due to what officials described as "human error." Officials said those tickets were honored because they were not discounted as a result of intentional manipulation by customers.
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