A number of SPAR shops cross the North of England have been forced to close following an "online attack" on its IT system.
The issue, which began on Sunday 5 December, saw a "major and widespread IT failure" after the suspected cyber attack on the entire Northern SPAR network.
It means stores cannot take card payments or use their stock control and accounting systems.
The retailer said the attack had hit all of the company’s IT systems, including staff emails.
As of Tuesday 7 December stores were still closed with one SPAR in Ribchester, Lancashire, saying IT specialists had decided more work was still to be done to reconnect the network.
It said: "After extensive testing yesterday the IT specialists decided NOT to proceed with any store connections last night.
"There was still more work to be done to ensure they are fully ready to commence this activity this morning."
The IT outage first hit on Sunday and technicians worked through the night trying to fix the problems.
The website for Preston food distributor James Hall and Co, which sends goods to nearly 600 Spar shops throughout the north of England, was also taken offline.
A SPAR spokesperson said: "At James Hall we are currently aware of an online attack on our IT systems.
"This has affected around 330 Spar stores across the north of England over the past 24 hours and we are working to resolve this situation as quickly as possible.
"It is currently impacting stores’ ability to process card payments meaning that a number of Spar stores are currently closed to shoppers or only taking cash payments.
"We apologise for the inconvenience this is causing our customers and we are working as quickly as possible to resolve the situation."
A number of stores were able to reopen on Monday, accepting cash only, with the Ribchester store telling customers it was only able to open its Post Office.
Posting on its Facebook page on Sunday morning, SPAR in Ribchester, Lancashire, said: "Due to a major & widespread IT failure across the entire Northern SPAR network, all Northern Spar stores will be closed for an unknown period of time."
It added: "Sadly the Spar store side of our business remains closed today, however our Post Office is able to be open.
"We will also be able to provide the saved newspapers to those customers who pre pay.We can also process parcel collections.
"Due to the stock control and accounting systems employed at our stores, we are unable to sell any shop items until our systems are restored.
"We apologise for this continued inconvenience and will update via social media as and when the situation changes."
The widespread store closures cover the whole of the north of England, with those in the North East and North Yorkshire also affected.