The FBI has reportedly alerted defence contractors, energy firms and educational institutions in the US about a sophisticated Iranian hacking operation.

In its latest warning, the FBI has asked businesses to contact the agency if they think their firms have been targeted by the attack.

Citing FBI’s confidential "Flash" report, Reuters noted that the report offers technical details regarding malicious software and techniques deployed in the attacks, in addition to suggestion on thwarting the hackers.

Without attributing the attacks to the Tehran government, the US agency noted that the hackers usually target victims through attacks from two IP addresses in Iran.

Iran has been augmenting its cyber security investments since 2010, after a Stuxnet computer virus hit its nuclear programme which was broadly considered to be have been launched by the US and Israel.

A recent report from Businessweek also reveals that Iranian hacker activists were behind a February 2014 attack on casino operator Las Vegas Sands, which crippled several servers with a destructive malware.