The U.S. Federal Bureau of Investigation said in a warning to businesses that it has identified increased scams targeting businesses working with foreign businesses that regularly perform wire transfer payments.

Fraudsters sought to steal $5.3 billion through schemes known as business email compromise from October 2013 through December, the FBI said in a report released Thursday. FBI's previous report said thieves attempted to steal $3.1 billion from October 2013 through May 2016.

The number of business-email compromise cases, in which cyber criminals request wire transfers in emails that look like they are from senior corporate executives or business suppliers who regularly request payments, almost doubled from May to December of last year, rising to 40,203 from 22,143, the FBI said.

The scam is carried out when a subject compromises legitimate business e-mail accounts through social engineering or computer intrusion techniques to conduct unauthorized transfers of funds.

Most victims report using wire transfers as a common method of transferring funds for business purposes; however, some victims report using checks as a common method of payment. The fraudsters will use the method most commonly associated with their victim's normal business practices. The scam has evolved to include the compromising of legitimate business e-mail accounts and requesting Personally Identifiable Information (PII) or Wage and Tax Statement (W-2) forms for employees, and may not always be associated with a request for transfer of funds, FBI said.

The United States is the biggest target market, though fraudsters have started to expand in other developed countries, including Australia, Britain, France and Germany.

The FBI has said that about one in four U.S. victims respond by wiring money to fraudsters. In some of those cases, authorities have been able to identify the crimes in time to help victims recover the funds from banks before the criminals pulled them out of the system.