The firm said it was “urgently investigating illegal and unauthorised access” to the personal data of some customers.
It is believed that the breach could affect up to 270,000 current and former customers - including 245,000 in the UK as well as a further 25,000 in Poland.
The stolen data includes names, addresses, bank account numbers, sort codes and phone numbers.
Following the alarm being raised, the firm started to contact customers on Saturday and has set up a dedicated phone line on 0207 138 8330 to offer support. Concerned borrowers should also reference the company’s FAQ page: www.wonga.com/help/incident-faq.
Borrowers are advised to alert their bank and ask them to look out for any suspicious activity. Wonga will also be informing financial institutions about the breach.
While the lender say that they believe that customer’s Wonga accounts are safe, they suggest that anyone concerned may wish to change their wonga.com password.
Customers are also advised to watch out for unusual online activity and beware of cold calls and emails asking for personal information.
A company statement read: “We are working closely with authorities and we are in the process of informing affected customers. We sincerely apologise for the inconvenience caused.”