WannaCry NHS attack (2017)
The WannaCry worm, using a leaked NSA exploit, hit Britain's National Health Service and encrypted systems at over a third of NHS trusts.
Tens of thousands of appointments and operations were cancelled; many trusts reverted to paper records.
Exposed how dependent healthcare is on unpatched systems and sparked a push for cyber resilience.
Demonstrates the human cost when healthcare IT goes down, even briefly.
