Royal Bank of Scotland has said its websites fell victim to a cyber attack after customers were unable to access online banking.
The group's website, which includes NatWest, was down for approximately an hour this morning and yesterday night following what the bank described as a "deliberate" surge in traffic in a cyber attack.
The problem has now been resolved and online services have returned to normality, according to the lender.
The bank said that the attack didn't pose a risk to clients.
A spokesman said: "Due to a surge in traffic deliberately directed at the NatWest website, customers experienced difficulties accessing our customers websites
"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."
Angry customers took it to Twitter to express their frustration using the hashtags #timetochangebank and #topbank among others.
The incident comes less than a a week after shoppers were unable to complete online payments coinciding with Cyber Monday- one of the busiest day of the year for online shopping.
The glitch left customers in the dark for hours and prompted an apology from RBS chief executive Ross McEwan, who admitted that the group had failed to invest in IT services for decades.
RBS said today's attack was not related to Cyber Monday's crash.
In May, RBS and Natwest customers experienced similar problems being unable to access their bank accounts on mobile.
The incident was followed by a major technical glitch in June, where key transactions, including payments and wages, appeared to go missing.
The group was forced to pay £175 million in compensation.
Additional reporting PA