The Co-op said it has shut off parts of its IT systems after an attempted hack.
It said some of its back office and call centre services have been affected but that all stores, including grocery and funeral homes, are trading as usual.
The retail firm said it is “working hard to reduce any disruption to our services” and thanked staff and customers for their patience.
The business owns more than 2,000 grocery stores and 800 funeral parlours across the UK.
It comes as rival Marks & Spencer continues to deal with the lengthy fallout of a major cyber incident.
M&S has been unable to process online orders since last Friday, after click and collect orders and contactless payments were first affected by the cyber attack. The Metropolitan Police have since confirmed they are investigating.
It is not known whether the hacks of the two retailers are related.
A Co-op spokesman said: “We have recently experienced attempts to gain unauthorised access to some of our systems.
“As a result, we have taken proactive steps to keep our systems safe, which has resulted in a small impact to some of our back office and call centre services.
“We are not asking our members or customers to do anything differently at this point. We will continue to provide updates as necessary.”
