Payday loan firm Wonga has suffered a data breach affecting up to 245,000 customers in the U.K. A further 25,000 customers in Poland may also be affected, according to the BBC.

A notification on Wonga’s U.K. website currently warns of “illegal and unauthorised access to limited personal data,” and says affected customers have been emailed about the breach.

According to an FAQ page on its website, the types of personal data that may have been compromised includes names, email addresses, home addresses, phone numbers, the last four digits of bank card numbers (but not the whole number) and/or bank account numbers and sort codes.

It says it does not believe customers’ Wonga account passwords were compromised but suggests concerned users change their password anyway.

Wonga is warning affected customers to be “extra vigilant” and to alert their bank of potential risk — though it says it will also be contacting financial institutions about the breach.

Given that the last four digits of bank cards can be used as part of the login process for online accounts, there’s a potential risk that breached data could be used to try to log into customers’ bank accounts.

We’ve reached out to Wonga with questions and will update this story with any response. Update: In a statement a spokesperson for the company told us: “Wonga is urgently investigating illegal and unauthorised access to the personal data of some of its customers in the UK and Poland. We are working closely with authorities and we are in the process of informing affected customers. We sincerely apologise for the inconvenience caused.”

There are no details about how the breach happened at this point, with Wonga saying only on its website that it is “urgently working to establish further details” and making a generic statement about the rise of “increasingly sophisticated” cyberattacks.

According to The Guardian, the company became aware of a problem last week but only realized on Friday that data could be accessed externally, and only started contacting affected customers on Saturday. The U.K.’s data protection regulator, the ICO, has apparently been informed of the breach — although it’s unclear when. An ICO spokesperson did not respond to the question, providing this statement instead: “All organisations have a responsibility to keep customers’ personal information secure. Where we find this has not happened, we can investigate and may take enforcement action.”

New European Union-wide rules on data breaches coming into force in May 2018 will require companies to swiftly (within 72 hours) notify data protection authorities of data breaches involving financial information — with fines of up to €10 million or 2 percent of a company’s global turnover for failures of compliance.

This is by no means the first time Wonga has attracted negative headlines. Back in 2014 the company had to write down $340 million in unpaid loans, following an investigation by the U.K.’s Competition and Markets Authority over its lending practices. It was also fined by the regulator for sending fake lawyers’ letters to customers in arrears.

Although Wonga attracted substantial tech investment for a real-time automated decision-making platform for affordability checks, it ended up having to write off the loans of 330,000 customers, and waive the interest and fees for a further 45,000 — raising questions about the efficacy of its algorithms.

Tightened criteria on short-term loans by the U.K. financial regulator ultimately shrunk the size of Wonga’s business, which saw losses double in 2015 — to £80.2 million.