A ransomware hack attack as left a hospital chain in the Washington, D.C. area still recovering days after its computer systems were infected with malicious software. MedStar Health serves hundreds of thousands of patients in the metro D.C. area. The cyberattack on March 28, Monday that hit 10 hospitals caused patients to get a voice message asking them to bring an up-to-date list of medications and allergies to the medical center in person.

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Ransomware is a type of malware that encrypts data. The demand for money usually asks victims to pay in digital currency such as Bitcoin so they can receive an electronic key and get their data back.

MedStar announced on March 31, Thursday that its IT systems were slowing coming back on line and medical records were already available, according to NBC News. It reported that since the hack the company had served over 6,000 patients.

However, some patients reported that their doctor appointments had been rescheduled or canceled. That was because doctors were unable to access medical records within the first couple days after the malware attack.

Cyber security experts report that ransomware is becoming a disconcerting new trend. In February a Los Angeles medical center paid $17,000 to get its system up and running after the malicious software infected its computer systems.

Since then similar attacks have happened in North America. They include medical centers in West Virginia, Kentucky, Canada, and others in Southern California.    

James Trainor is the FBI's top cybercrime official. He says the number of cases rose sharply last year and in Q1 2016, which has resulted in $24 million in ransom costs alone.  

The FBI suggests that ransomware victims not pay the demand for money, but individuals and companies often end up making the payment.

Kevin Fu is an associate professor at the University of Michigan. He explains that the threat of ransomware in the health care industry is different than other attacks because the results are worse, according to MIT Technology Review.

Fu notes that it can be annoying to lose email, but patient records are needed to treat people in hospitals. For example, the cyber-attack at LA's Hollywood Presbyterian Hospital required some patients to be moved to other medical centers.   

Here's a video about the hack of the LA medical center: