Monzo have been urging more than 500,000 customers to change their pins after it was revealed that the challenger bank discovered an internal flaw in its system.
The incident happened when Monzo staff were allowed to see all personal information for these customers.
The fintech darling had around a fifth of its customer base affected by the incident, and made it possible for certain members to have the pin codes easily accessed by engineers.
Monzo has stated that it has deleted all the improperly stored information today.
In an email to its customers, Monzo wrote: “We’ve fixed an issue that meant we weren’t storing some customers’ PINs correctly. There’s been no fraud on your account because of this, but you should update your app and change your PIN as a precaution.
“We keep a record of your PIN so we can check you’ve entered it correctly. We store them in a particularly secure part of our systems, and tightly control who in the company can access them.
“On Friday 2nd August, we discovered that we’d also been recording some people’s PINs in a different part of our internal systems (in encrypted log files). Engineers at Monzo have access to these log files as part of their job.
“We’ve deleted any information that we stored in this way, and we’ve released an update to the Monzo app. As soon as we discovered the bug, we immediately made changes to make sure the information wasn’t accessible to anyone in Monzo. We’ve confirmed your account hasn’t been used for fraud because of this issue. Just in case though, you should update your app and change your PIN as a precaution.”