The hackers who broke into Franklin, Tenn.-based Community Health Systems' network and stole 4.5 million patients' information did so using the Heartbleed Internet bug, according to a Reuters report.
The Heartbleed bug allows hackers to access computer systems using OpenSSL encryption software without leaving a trace.
The hackers used stolen employee credentials to log into the network. They then hacked into a database where they were able to steal the records, according to the report.
The CHS data breach is the largest known cyberattack using Heartbleed, according to the report.
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