U.K.-based Monzo Bank Ltd. said it corrected a security flaw which led to less than a fifth of its customers' personal identification numbers being incorrectly stored in its systems.

The digital lender discovered Aug. 2 that it had been recording some clients' PINs in encrypted log files, which were visible to the company's engineers. Monzo Bank said once the flaw was detected it made changes to the system early Aug. 3 and deleted the sensitive information by Aug. 5 to prevent it from being accessed.

The company, which is valued at just over £2 billion, noted it checked all the affected accounts and confirmed no fraud was committed.

Monzo Bank added it requested all of its customers to change their PINs to a new number and update their Monzo mobile application to the latest version.