Customers of leading banks and building societies are being targeted in a fraudulent e-mail campaign that tries to fool people in to handing over their account details.
Lloyds TSB and Nationwide were the latest banks to be the subject of the swindle.
Concerned recipients of the e-mail alerted Lloyds TSB early yesterday morning and Nationwide customers received e-mails over the weekend.
Halifax, NatWest, and Barclays have also been used in the same scam in recent days.
At least 300 people contacted Lloyds TSB yesterday to say they had been sent suspect e-mails. The e-mail - thought to originate in Eastern Europe - appears to be from the bank in question and contains a link to the bank's website.
But when the website is accessed via the link, a message is displayed that asks customers to enter their internet banking user ID and password. Recipients of the e-mail are not necessarily customers of the chosen banks, but appear to be on a random list of names.
The banks have taken steps to shut down the replica website to which the e-mail provides a link.
Lloyds TSB has made customers aware of the problem through its website, asking them to ignore the e-mail.
The bank yesterday said a handful of customers had been misled in to passing over their details. Their accounts have now been suspended and the bank said it was confident that no fraud had taken place.
Nationwide said it did not believe any customers had given their details away.
A spokesman for Lloyds TSB said: "This is different to anything we have ever seen before. We are advising everyone to delete the e-mail if they receive it and we want customers to know that we would never ask for their details in this manner. We have briefed all our call-centre staff to make sure they can advise concerned customers.
"Our site is very secure and we take all actions like this very seriously. The fact that we have not had any fraud committed is a sign of how quickly we can deal with a problem like this."
People in the US, Australia New Zealand and continental Europe have also been targeted in the scam in the past year.
Lloyds TSB and Nationwide have set up a helpline for any customers that fear they may have been affected.
Lloyds TSB has informed the National High Tech Crimes unit, which is investigating the incident.