Royal Bank of Scotland said its websites were the victim of a cyber attack that left some customers unable to access their accounts in the group’s second computer crash in less than a week.
The group’s sites went down for about an hour after a “deliberate” surge in internet traffic aimed at its NatWest website, according to the lender.
It said sites were now back up and running and there was no risk to customers.
A spokeswoman said: “Due to a surge in internet traffic deliberately directed at the NatWest website, customers experienced difficulties accessing some of our customer websites today.
“This deliberate surge of traffic is commonly known as a distributed denial of service (DDoS) attack.
“We have taken the appropriate action to restore the affected websites – at no time was there any risk to customers.”
It comes just days after an embarrassing IT failure for the group on the busiest online shopping day of the year.
RBS boss Ross McEwan admitted it had failed to invest properly in systems for decades as he apologised for the glitch on Monday, which left customers of RBS and its NatWest subsidiary unable to use credit and debit cards for three hours, while the banks’ websites and smartphone apps were also affected.
It came on so-called Cyber Monday, when retailers expected the highest number of online transactions to take place ahead of Christmas – and prompted a flurry of card users to take to Twitter to vent their anger.
RBS said today’s cyber attack was not related to the issues on Monday, adding that banks around the world are regularly subjected to this type of deliberate attempt to bring systems down and disrupt customer access.
But the group has had a run of IT woes over the past two years.
In May, another glitch left RBS and NatWest customers using mobile apps unable to access their accounts online.
That followed a major fiasco in June last year which saw payments go awry, wages appear to go missing and home purchases and holidays interrupted – and cost the group £175 million in compensation.