More than £500m was stolen from customers of British banks in the first half of 2018, figures have shown.
Industry group UK Finance said £145m of that was due to authorised push payment (APP) scams, in which people are conned into sending money to another account.
But £358m was lost to unauthorised fraud, which includes transactions made without account holders' knowledge.
Unauthorised fraud victims are usually refunded by their banks, but most victims of APP fraud do not get their money back.
This is because current legislation means they are liable for any losses incurred if they authorise a payment themselves.
"Purchase scams", in which people are duped into paying for products or services that do not exist, were the most prevalent form of APP fraud reported in the first six months of 2018.
These scams often happen online, and examples include payments made for cars or holidays that are never delivered or provided.
There were also 3,866 reported cases of impersonation scams, in which criminals pretend to be from a financial institution or law enforcement, and trick account holders into transferring money.
During the first six months of 2017, APP scams led to £101m in losses, but UK Finance said this year's £44m increase was partly down to four more banks reporting data.
How to protect yourself against fraud
When you transfer money from your bank account, you are asked to enter three pieces of information: the name of the payee, their account number, and the sort code.
However, only the last two are cross-checked by the bank. So putting in the correct name is no guarantee that person will get the money.
UK Finance offers the following advice:
- Never disclose security details, such as your PIN or full banking password
- Don't assume an email, text or phone call is authentic
- Don't be rushed - a genuine organisation won't mind waiting
- Listen to your instincts - you know if something doesn't feel right
- Stay in control - don't panic and make a decision you'll regret
The group's managing director for economic crime, Katy Worobec, said the new figures underlined that fraud was a "major threat" to the UK, and added that the "proceeds go on to fund terrorism, people smuggling and drug trafficking".
Ms Worobec also emphasised that two-thirds of all unauthorised fraud was successfully thwarted by UK financial institutions.
But Gareth Shaw, of the consumer group Which?, said the banks' efforts to tackle fraud had been "woefully insufficient".
APPs were the subject of a "super-complaint" made in September 2016 to regulators by Which?, which has been calling for banks to shoulder more responsibility when victims are tricked in this way.
"They have not done enough to protect their customers, who continue to lose life-changing sums of money to ever-more sophisticated crooks," Mr Shaw said.
But he welcomed plans by the Payments System Regulator to introduce a reimbursement scheme for victims of APP fraud.