Customers trying to order groceries online are presently being met by a holding page warning them that the site has been “temporarily frozen”.
The grocer said it is contacting all customers directly whose deliveries have been affected.
One customer waiting for a delivery, who spoke to the BBC, said she was only contacted about the problem 15 minutes into her hour-long delivery slot.
Sainsbury’s other e-commerce services, such as its wine web site, do not appear to be affected.
No comment was available from the retailer.