Three U.S. hospitals were hit this week by "ransomware" attacks that brought down their systems, according to NBC News.
The servers for Chino Valley Medical Center and Desert Valley Hospital, both in California, and Methodist Hospital in Kentucky were all attacked by malware.
Ransomware is a strain of malware that encrypts data on infected systems, then asks users for ransoms in exchange for their data.
As of Wednesday, the two hospitals in California were brought back online. The third hospital did not immediately return calls from NBC News.