Overview#Class-Break a particular security vulnerability that breaks not just one system, but an entire class of systems.
Electronic door locks, like the ones you now find in hotel rooms, have different vulnerabilities. An attacker can find a flaw in the design that allows him to create a key card that opens every door.
If he publishes his attack software, not just the attacker, but anyone can now open every lock. And if those locks are connected to the Internet, attackers could potentially open door locks remotely -- they could open every door lock remotely at the same time. That is an Example of a Class-Break.