What caused the computer failure at Ulster Bank

Ulster Bank said on Monday it was making progress to deal with the backlog and delays in its payments systems caused by a technology problem at its RBS parent group. The BBC News website looks at how the computer failure happened and what the bank is doing to restore a full service.

How are transactions usually processed?

Every evening RBS processes that day's transactions across its entire banking businesses, an average of 20m transactions.

They are processed in batches through automated systems. In normal conditions the overnight processing is done before business resumes the following day.

What caused the computer failure?

RBS said a problem was created when maintenance on systems that are managed and operated by staff in Edinburgh caused an error.

This error caused the automated processing to fail on the night of 19 June.

Processing delays built up and staff had to intervene manually.

They were unable to access the record of transactions that had been processed up to the point of failure.

Finding out at what point processing had stopped delayed subsequent processing and created a backlog.

As a result a significant number of customer account balances did not update as they should have from 19 June.

What progress has the bank made to restore a full service?

The backlog had to be cleared before the bank could begin to return the systems to normal.

To restore a normal service, the batches had to be brought back into sequence.

The bank said payments follow in sequence after those of NatWest and RBS. This is because of the way the technology was set up when the three banks were integrated.

RBS said it regretted any confusion this might have caused.

When will normal service resume for Ulster Bank customers?

Staff are now working to catch up on the backlog.

The bank said customers should see their balances updating during this week.

Ulster Bank said normal service will take some further time as experience from dealing with the same issues in RBS and NatWest suggests that there may be "bumps along the road".

How will customers be kept informed?

Ulster Bank said it would issue a media update every day on its websites, via Twitter @UlsterBankGroup, in call centres and branches.

Will there be an investigation?

RBS said it would carry out a full and detailed independent investigation into the causes of the problem, once the critical system recovery tasks were completed.

Will customers be compensated?

Ulster Bank said it was committed to ensuring that no-one would be left permanently out of pocket as a result of the computer failures.

Any customers affected should contact the bank.