The China-linked cyber intruders broke into Exchange by finding a handful of coding errors that gave them entry into Exchange servers and then allowed them to take control.

"Ransomware has become a huge business, and as in any business, in order to scale it, they're coming up with innovative models," said Dmitri Alperovitch, head of Silverado Policy Accelerator.

The NBA's Houston Rockets were hit by a ransomware attack earlier this month. Now it's the Washington, D.C., police department. The common thread is an unknown ransomware group called Babuk.

The Western intelligence agencies say they believe the hackers are part of the Russian group informally known as Cozy Bear. The intelligence agencies refer to it as APT29.

The group that targeted the WHO is known to perform a significant amount of reconnaissance on the configurations and the systems of their targets, and it could likely be a state-sponsored group.