British digital bank Monzo has urged nearly half a million of its customers to change their card PIN after detecting a security bug in their system.

In a blog post, Monzo said that it usually stores customers’ PIN to authenticate transactions and payments. However, last week it detected that some of the customer PINs were recorded in encrypted log files, which can be accessed by its engineers.

Following the detection, the data was deleted and the bank released updates of Monzo apps. It also checked all accounts and claimed that the data was not compromised.

However, as a precautionary measure it informed the affected customers to change their card PIN from an ATM.

“The issue affected less than a fifth of UK Monzo customers. If we’ve contacted you to tell you that you’ve been affected, you should head to a cash machine to change your PIN to a new number as a precaution,” the blog post added.

According to The Guardian report, around 480,000 customers were requested to change their card PIN.

Monzo, which has more than 2.5 million users, is one of the fastest growing digital lenders in the UK.

In June this year, the lender announced its annual results. It registered a loss of £47.2m in twelve months to February 2019. The figure is a significant increase over a loss of £30.6m for the year ago period.