A cyber attack brought down the websites of Portugal's largest food retailer Continente and affected some services in its stores on Wednesday, said the company, which is owned by the Sonae group, without providing further detail.
Its main website for online shopping was down, displaying the message 'Under maintenance. Please try again later'.
In a statement, Modelo Continente, which runs a stable of around 300 hypermarkets and large supermarkets in Portugal, said that the hacker attack on its systems was "affecting some communications on commercial sites and some in-store services."
It said that its teams were investigating the disturbance created and working to restore, 'as soon as possible', the normal functioning of its activity.
Local media said payments at stores were largely unaffected, but clients reported problems getting their shopping bills and using the Continente loyalty cards.
Sonae shares were little changed at €1.013 euros on the Euronext Lisbon stock exchange.
Since the beginning of this year, two other large Portuguese companies, the media and television conglomerate Impresa and telecom Vodafone Portugal, have also suffered attacks by hackers.
In July of last year, grocery store chain Coop Sweden closed all its 800 stores after a ransomware attack on an American IT provider left it unable to operate its cash registers.