MuddyWater has been attacking targets around the world for years, according to the U.S. and other western governments.

The group allegedly has targeted the defense, local government, oil and natural gas and telecommunications sectors in places including North America.

The release marks the U.S. government's first attribution of the group's activity to the Iranian government.

The activity is focused on targets in Israel, Saudi Arabia and elsewhere.

MuddyWater is targeting government agencies, academia and the tourism industry.

While other hacking teams associated with Tehran have gained notoriety for data-wiping attacks, MuddyWater as been relentless in its spying efforts.

The hackers could be prepositioning for a retaliatory attack, or biding their time to collect intelligence, researchers say.

Undeterred by the reported dumping of its data online, an Iran-linked hacking group has been using malicious documents and files to impersonate government entities.

The group bears a resemblance to MuddyWater.

Researchers found the suspected Iranian group on the same embassy network as Fancy Bear.