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

"We could not find any evidence that these tools were used previously, or attribute them to a specific threat actor," Check Point researchers said.

It’s an example of how, alongside the violence that has long marked the Israel-Palestine conflict, there are often much subtler efforts by digital spies to access networks.

The emails politely ask users in fluent English to enable Microsoft Excel features that allow the code to execute.

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.