The Co-op has shut down parts of its IT systems in response to hackers attempting to gain access to them.
It said the “proactive measures” it had taken to fend off the attack had had a “small impact” on its call centre and back office.
Meanwhile, The Metropolitan Police has confirmed it’s looking into the major cyber attack at fellow retailer Marks & Spencer (M&S).
“Detectives from the Met’s cyber crime unit are investigating,” it said in a statement.
It is not known whether there is any link between the two incidents.
There are more than 2,500 Co-op supermarkets in the UK, as well as 800 funeral homes. It also provides food to Nisa shops.
A spokesperson confirmed its shops and funeral homes were operating as usual following the attempted hack.
“We are working hard to reduce any disruption to our services and would like to thank our colleagues, members, partners and suppliers for their understanding during this period,” they said.
“We are not asking our members or customers to do anything differently at this point.”
It comes as M&S enters the second week of a cyber attack that has caused chaos costing it millions of pounds in lost sales.
The retailer has not said what took out its online ordering systems and left empty shelves in stores, but the BBC has been told by security experts that ransomware called DragonForce was used.
Ciaran Martin, the founding Chief Executive of the National Cyber Security Centre (NCSC), told the Today programme on BBC Radio 4 on Wednesday it had “serious” consequences for M&S.
