NatWest says that a Distributed Denial of Service attack knocked out its site on Friday, leaving customers unable to access online banking services.
The Royal Bank of Scotland-owned outfit says in a statement: "The issues that some customers experienced accessing online banking this morning was due to a surge in internet traffic deliberately directed at the website.
"At no time was there any risk to customers. Customers experienced issues for around 50 minutes and this has now been resolved."
The latest tech issue comes just six weeks after the bank suffered an embarrassing breakdown that caused over 600,000 transactions and hundreds of thousands of pounds in payments to go missing.
While the bank's IT team scrambled to fix the problem, long-suffering customers took to social media to vent.
NatWest parent RBS and Ulster Bank were hit with a £56 million fine by regulatory authorities last year over a computer malfunction in 2012 that locked customers out of accounts and knocked out payments processing systems.
At the time, RBS chief Ross McEwan admitted that the bank had failed to invest properly in its IT system for decades and promised to invest an extra 750 million pounds by the end of 2015 to enhance the security and resilience of its IT systems.
Following last month's meltdown, RBS bosses pledged to invest a further £150 million a year to improve the resilience of its IT systems.