NatWest has been forced to suspend some of its UK online banking services after coming under attack from a previously undocumented phishing scam.

Customers logging on to NatWest's online banking service are being advised that they cannot create or amend third-party payment mandates or create standing orders.

According to IT security firm Sophos, the bank has taken the measures following the emergence of an email which masquerades as an official software update from the bank.

It is feared that this may dupe online customers into divulging their passwords and unwittingly provide access to their bank accounts.

The home page of NatWest's site warns: "Fraud Alert. Do not enter any online banking details into pop-ups/new windows that may appear in front of this home page."

Graham Cluley, senior technology consultant at Sophos, said: "NatWest customers, and indeed anyone banking online, should remember to be extremely suspicious of unexpected emails that appear to have come from their bank, and never to click on links contained within them.

"It is good to see a financial institution taking quick action to protect its customers from potential fraud."

More information on how to avoid phishing attacks can be found here.