Crooks are posing as solicitors to scam millions of pounds out of homebuyers in a so-called Friday afternoon fraud.
The Law Society of England and Wales said that the scams were on the rise amid a boom in the property market.
The criminals hack into e-mails between solicitors and their clients and then, as the money is about to be moved, impersonate the lawyer and ask the homebuyer to pay the house deposit or balance into an account they control.
Solicitors can also fall victim to the scheme when transferring money to their clients, though there is a better chance of the funds being recovered under professional indemnity insurance.
It is known as Friday afternoon fraud because that is the day many property sales complete and funds in a transaction are transferred.
In one case, a homebuyer was conned out of £640,000, most of which was never recovered.
Hacks of conveyancing transactions are the most common form of cybercrime in the legal sector, according to the Solicitors Regulation Authority, with homebuyers reporting losses of £7m last year.
