On December 1, fans flooded Adele.com to purchase advance tickets to Adele’s 2016 concert tour. However, a lot of fans in the UK were alarmed to see other customers’ details on the tickets site. Was the site hacked?

No, it wasn’t. Ticketing company Songkick admitted that the technical glitch was “due to extreme load.”

“We take the security of our users and Adele’s fans very seriously, and we apologize for the alarm we have caused to those purchasers who experienced issues,” Songkick said.

According to Billboard, the ticketing company had a strategy to avoid “secondary market ticket sales” or what they call as “touts.” Songkick was formerly an artist discovery platform which recently merged with “direct-to-fan” ticketing company CrowdSurge.

Adele.com broadcasts that they will not tolerate the reselling of tickets, Music Business Worldwide wrote. The team behind the British singer came up with a plan to block “touts” through a pre-sale registration process. In order to purchase concert tickets, fans had to put in their personal details on Adele’s website.

“We were carefully monitoring all of the registrations to try and spot anything suspicious,” Adele’s manager Jonathan Dickins said. According to experts, such process managed to kick out about 15,000 to 18,000 “touts” in the UK.

But in their effort to achieve the “zero tolerance” goal, the pre-sale faced problems on the site. Fans claimed to see other customers’ personal data, such as credit card details, upon checkout.

Emma Harris from Woking told BBC that when they were about to purchase the tickets, the customer details were already filled. The screen showed the name, address, and credit card number of another customer.

“It’s definitely worrying, as I know myself and a lot of friends of mine have paid with our credit card details and we don’t know who they’ve been exposed to.” Harris said.

Security consultant Graham Cluely said that the technical glitch was impossible. Cluely mentioned that the codes on the website must have been written insecurely. He urged customers to be extra cautious.

According to Adele.com, registration for the next pre-sale will reopen on December 3.