It's being called the largest ever breach of protected patient health information by a government-regulated medical company in America's history. Change Healthcare, owned by UnitedHealth Group, fell victim to a cyberattack eight months ago, but revealed on Thursday that 100 million people had been impacted. That surpassed the previous recordholder for worst breach of US patient data: a 2015 episode at Anthem Inc. that compromised 78.8 million individuals. The first official report by Change Healthcare, which manages revenue and payments for medical providers, estimated in July that only 500 people had been compromised. Now, the scope of the February 21...