The smartphone bank Revolut claims to have been the victim of a cyber attack.
This emerges from a communication from the British fintech to the supervisory authorities in Lithuania.
Revolut operates in Europe with a Lithuanian banking license.
Revolut spokesman Michael Bodansky told the TechCrunch portal that an unauthorized third party "gained access to the data of a small percentage (0.16 percent) of our customers for a short period of time".
Revolut discovered the attack late in the evening of September 11 and was able to isolate the attack by the following morning.
The notice to regulators in Lithuania said Revolut's security team acted quickly to stop access to the company's customer data.
The Revolut spokesman declined to say exactly how many customers were affected.
On its website, the company states that it has around 20 million customers;
0.16 percent would correspond to about 32,000 customers.
However, in Revolut's communication to the Lithuanian authorities, the company states that 50,150 customers were affected by the security breach.
In a message to affected customers posted on Reddit, the company said "no card details, PINs, or passwords were compromised."
However, the notice states that the hackers likely accessed partial card payment details, as well as customers' names, addresses, email addresses, and phone numbers.