It has been reported by the BBC that Tesco's website and app are now up and running again, following a service outage that began on Saturday.
The retail giant's services had crashed after what Tesco said were attempts "to interfere with our systems".
The possible hack at Britain's biggest supermarket began with shoppers unable to order goods and track deliveries.
Tesco initially said there was "an issue", but in a Sunday update said there had been deliberate disruption.
The supermarket later confirmed on Twitter that its groceries website and app were back up and running, but it was temporarily using a "virtual waiting room" to manage the high volume of traffic.
Tesco said the attempts to compromise its systems were made overnight from Friday to Saturday, but was not more specific.
According to Downdetector, which monitors website outages, shoppers began reporting issues early on Saturday morning.
The scale of the problem, and whether the issue was nationwide or only in certain areas, remained unclear on Sunday night.
Shoppers complained over the weekend about a lack of information, with many wanting to know how to cancel orders and whether they can get money back.
Earlier on Sunday, a Tesco spokesperson said: "There is no reason to believe that this issue impacts customer data and we continue to take ongoing action to make sure all data stays safe.
"Since yesterday, we've been experiencing disruption to our online grocery website and app.
"An attempt was made to interfere with our systems which has caused problems with the search function on the site. We're working hard to fully restore all services and apologise for the inconvenience."
Meanwhile, shoppers were trying to change or cancel deliveries, or switch to other supermarkets.
