By Jose Pagliery @Jose_Pagliery August 18, 2014: 3:25 PM ET
NEW YORK (CNNMoney)
Community Health Systems, which operates 206 hospitals across the United States, announced on Monday that hackers recently broke into its computers and stole data on 4.5 million patients.
Hackers have gained access to their names, Social Security numbers, physical addresses, birthdays and telephone numbers.
Anyone who received treatment from a physician's office tied to a network-owned hospital in the last five years -- or was merely referred there by an outside doctor -- is affected.
The large data breach puts these people at heightened risk of identity fraud. That allows criminals open bank accounts and credit cards on their behalf, take out loans and ruin personal credit history.
The company's hospitals operate in 28 states but have their most significant presence in Alabama, Florida, Mississippi, Oklahoma, Pennsylvania, Tennessee and Texas.
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Community Health Systems (CYH) hired cybersecurity experts at Mandiant to consult on the hack. They have determined the hackers were in China and used high-end, sophisticated malware to launch the attacks sometime in April and June this year.
The FBI said it's working closely with the hospital network and "committing significant resources and efforts to target, disrupt, dismantle and arrest the perpetrators."
Federal investigators and Mandiant told the hospital network those hackers have previously been spotted conducting corporate espionage, targeting valuable information about medical devices.