The Co-op apologised after hackers accessed and extracted data of a 'significant number' of customers, including names and contact details.
The hackers did not access passwords or financial information such as bank or credit card details; the National Cyber Security Centre and the National Crime Agency are assisting in the investigation.
Co-op reassured members that their accounts are unaffected, but advised them to keep passwords safe; data leaked did not include sensitive financial information.
The Information Commissioner’s Office is making inquiries, advising customers to use strong passwords and not reuse them across multiple accounts.