A Hollywood hospital has reportedly been struck by ransomware—a malicious software program that locks down computer networks and holds them for ransom.

Hackers targeted the IT systems at Hollywood Presbyterian Medical Center. The systems have been offline for more than a week since the hospital president and CEO Allen Stefanek declared an “internal emergency” on Feb. 5, according to NBC Southern California.

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The hackers have apparently demanded more than $3 million in Bitcoin, a digital currency common in cases of cyber ransom, in order to unlock the affected data, according to local news outlets NBC and Fox 11 Los Angeles.

Ransomware attacks are an increasingly common and lucrative scheme for cybercriminals. They have struck police station systems, corporate networks, and the personal computers of countless Internet users.

An attack works by encrypting the data on a computer system, rendering it inaccessible to users. Criminals then extort victims in exchange for a decryption key.

Attempts by Fortune to reach the hospital’s public relations office were met by an answering machine. The pre-recorded messaged asked to leave contact information and “any questions you may have regarding recent cyber attack.”

“We want to assure you that patient care has not been compromised as we continue to address this incident,” the message said.

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An unnamed doctor told NBC Southern California that employees have no access to email and are communicating via “jammed fax lines.” The doctor also reportedly said that “the computers are essential for documentation of patient care, transmittal of lab work, sharing of X-rays and CT scans,” and that medical records were inaccessible.

Hospital officials told NBC that they have looped in the FBI and the Los Angeles Police Department and have hired computer forensics experts to investigate the attack.