Action Fraud has warned of a new tool in the arsenal of online fraudsters.
Cunning criminals are using background hold music in a bid to make their scam calls more convincing.
The City of London Police's National Fraud Intelligence Bureau (NFIB) spoke to a convicted fraudster, who explained: "The banks say they would never call and ask for your account details or PIN numbers.
"My advice is never speak to anyone who calls you about your account, even if there is background music or other similar factors.
"If you have any concerns, go to a branch or hang up and call the bank direct."
Stephen Proffitt, deputy head of Action Fraud, added: "Fraudsters are constantly developing new ways to make their calls more convincing so members of the public need to remain vigilant.
"If you receive a cold call purporting to be from your bank, always end the call as soon as possible and call your bank back using the number on the back of your bank card or statement and ask to be put through to the fraud team. Tell them exactly what has just occurred.
"If you believe your bank details may have been compromised, you should report this to your bank immediately."