Hackers breached the U.S. Securities and Exchange Commission's computer system last year by taking advantage of companies that used authentic financial data when they were testing the agency's corporate filing system, according to sourcesr.

The Federal Bureau of Investigation and the U.S. Secret Service have since launched an investigation into a 2016 hack into the SEC'S EDGAR system, several of those people said.

The sources spoke anonymously because it is not a public investigation.