Ransomware scum have crippled a Hollywood hospital, bringing critical machines to a crashing halt and demanding US$3.6 million ransom.

Hollywood Presbyterian Medical Center declared an emergency as machines critical to CT scans, laboratory, and pharmacy work went offline over the last week, pushing staff back to pen and paper.

Chief executive Allen Stefanek told broadcaster NBC LA the problems were "significant".

He maintained impact to patients was limited.

"It was not a [targeted] malicious attack, it was a random attack," Stefanek says.

The ransomware variant used in the attack has not been named. It would likely need to be the latest variant of Cryptowall if attackers were to stand any hope of having the mind-blowing ransom paid, as many other ransomware packages contain fatal crypto design flaws.

Patients have been forced to travel an hour's drive to collect lab tests. Some reports say the hospital has reverted to fax machines for communication with the outside world.

The FBI has been called in to investigate.

Ransomware attackers have to date remained elusive. It is thought that only a small number of criminals are behind some of the most prolific ransomware malware such as Cryptowall.

Interpol has formed an international ransomware task force in a bid to identify the attackers. ®