@SerendipityJane - can you please explain why the fact chip and pin was still working is illuminating? I don't know what in the systems is different.
@NoWordForFluffy - the fact the CEO has put his name to 2 emails they've sent out shows how serious this was. It was important to contact everyone and acknowledge the issue as quickly as they were able.
They're saying it was a software update. If it was in-house then whoever decided to schedule it for overnight Friday to Saturday is an idiot and should be sacked. Even in a major 7 days a week retailer, there are unlikely to be the people available in IT, etc to resolve problems. If the software update was carried out by external provider then 1. I would expect it to be moved to a potentially less disruptive time in a supermarket retailer because you can never guarantee these things go smoothly and 2. it shows a level of arrogance that it would go smoothly.
I'd expect Sainsbury's to give details of exactly what happened in due course. If their systems are not robust enough that is a serious failure. If there was a cyber attack then this means they are vulnerable and need to be able to show what they are doing to avoid a recurrence.
As Sainsbury's is a FTSE100 listed company this is really, really embarrassing and they'll need to address it in the Annual Report. The business has to have a high level risk assessment and contingency plans so all of that will need to be reviewed. Be interesting to see what effect this has on the share price when the market opens tomorrow.
Given the posts on this thread, I'm glad I didn't go to the store yesterday. I really feel for all the Sainsbury's staff who had to deal with this yesterday and are potentially still dealing with it now. Retail work is not easy and even at the best of times customers can be awful.