The boss of Marks & Spencer has told customers the retailer is "working day and night" to manage the cyber attack that has forced it to temporarily shut down its online operations.
Stuart Machin said he was "really sorry" for the disruption to services, but did not say when normal business would resume.
M&S's problems began over the Easter weekend, and last week it confirmed it was dealing with a "cyber incident" and paused online orders on its website and apps.
The Co-op and luxury department store Harrods have also been targeted and the National Cyber Security Centre (NCSC) has urged retailers to be vigilant.
In his message, Mr Machin said: "We are working day and night to manage the current cyber incident and get things back to normal for you as quickly as possible."
He also thanked customers for "all the support you have shown us".
The cyber attack has already had a significant impact on the retailer, as online transactions account for about a third of its clothing and home sales. On average, £3.8m is spent on clothing and home products on its website and apps every day.
There have also been gaps on the food shelves in some stores after the firm took some of its systems offline in an attempt to manage the attack, while its loyalty scheme and gift card payments have been disrupted too.
Analysts have pointed out that M&S risks losing out to rivals, as online shoppers can quickly switch to other retailers' websites.
The problems have also coincided with a period of warmer weather, when people are likely to want to buy new summer clothes.
M&S shares dropped almost 2% on Friday morning, and are now down about 5% from the point when the company first disclosed its IT systems had been disrupted.
