Most home buyers need to transfer money to the escrow company to complete the down payment the day before closing. The common way to do that is with a "wire transfer" – an electronic transfer from the buyer's bank to the escrow company.
The escrow company will send "wire transfer instructions" to the buyer to send to their bank well in advance of the transaction. The instructions consist of routing and transit numbers, account numbers and lots of other numbers and information to be sure the money gets to the right account at the escrow company.
The fraud begins when the escrow company sends an email to the buyer with new wire transfer instructions, except it's not really from the escrow company (even though it looks like it is). The email has actually comes from a criminal who has hacked the buyer's email account. If the buyer gives their bank the "new" instructions, the money is transferred to the hacker's account, usually in a foreign country and impossible to recover. .
Escrow companies almost never change wire transfer instructions. If you received such a communication, call your escrow officer directly.