The Federal Bureau of Investigation has warned U.S. businesses to be on the alert for a sophisticated Iranian hacking operation whose targets include defense contractors, energy firms and educational institutions, according to a confidential agency document.

The operation is the same as one flagged last week by cybersecurity firm Cylance Inc. as targeting critical infrastructure organizations worldwide, cybersecurity experts said. Cylance has said it uncovered more than 50 victims from what it dubbed Operation Cleaver, in 16 countries, including the United States.

The FBI's confidential "Flash" report, seen by Reuters on Friday, provides technical details about malicious software and techniques used in the attacks, along with advice on thwarting the hackers. It asked businesses to contact the FBI if they believed they were victims.