The bright orange pre-loaded mastercard is used widely across the world.
Monzo, one of the biggest digital banks in the world has just revealed a huge security fail in the system that has left hundreds of thousands of customers at risk.
The error meant that unauthorised staff had access to customers' PIN codes for MONTHS, and the company has since urged users of the bank to change theirs.
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This is down to Monzo not storing some of the PINs properly, but the flaw has since been fixed.
The digital bank, which works alongside an app, has contacted over half a million of their customers urging them to change their PINs as soon as possible.
The email reads: “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."
They continued: “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.”
They added that this advice to update the codes is just a "precaution", and that "there’s been no fraud on your account because of this."
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