A new phone scam - known as number spoofing - is netting millions of pounds for fraudsters, consumers are being warned.
Financial Fraud Action UK (FFA UK) said the scam has become increasingly common in recent weeks.
Typically criminals fool people into thinking they are talking to their bank, or the police, on the phone.
To help gain the target's trust, they display a fake number on the phone's caller ID screen.
They then persuade the victim to hand over details of their bank account, or passwords, or suggest that they move money to keep it safe.
Using those personal details, they then steal money from that person's account.
Frequently it is businesses which are being targeted, as well as some well-off individuals.
"There's a big surge in criminals using this," said an FFA UK spokesman.
He said they had seen hundreds of such cases, with some companies losing as much as a million pounds.
When indulging in phone "spoofing", criminals will often draw attention to the number that is showing on the recipient's screen.
Officials warn people to watch out for such odd behaviour, as it is a big clue that something is wrong.
"Remember that if a caller is trying to draw your attention to the number on your phone display, it's very unlikely the call is genuine as there is no legitimate reason to point it out," said Craig Jones of the FFA.
The technology being used has existed for a number of years, but fraudsters have only recently started using it.
"It's not difficult for the criminals to fake a caller ID," said Mr Jones.
Earlier this month some of Britain's High Street banks launched a campaign to warn consumers about the dangers of "vishing" - otherwise known as voice phishing.
That is when fraudsters telephone victims, to try to get them to give out details of their accounts.
The campaign listed eight things a bank will never ask its customers to do, including asking for details of PINs or passwords.