A chain of hospitals serving hundreds of thousands of patients in the Washington, D.C. area is struggling to get back to normal, after it was hit with what's known as a "ransomware" attack.
Ransomware is a strain of malware that encrypts data on infected machines, then typically asks users to pay ransom in hard-to-trace digital currency to get an electronic key so they can retrieve their data.
A cyberattack forced MedStar Health to shut down computers Monday at ten hospitals in the Washington, D.C. area. Many patients with appointments got this voice message: "Our computer systems are still down, so we need you to bring a list of current medications and a list of allergies."
On Thursday the company said the system is gradually coming back, with medical records again online.
"MedStar is not only continuing toward full restoration of our major IT systems, but it has also maintained its promise to meet the care of the communities we serve," the hospital chain said in a statement. "Since Monday morning, we have seen more than 6,000 patients in our hospitals and ambulatory centers."
Even so, some patients said their appointments had been cancelled or rescheduled because doctors could not access medical records in the first few days of the computer attack.
A suburban Washington woman, who asked that her name not be used, said her husband was forced to miss three days of cancer radiation therapy.
"I was shocked. And this being new to us, I have no idea what that means by not having it."
Ransomware is a troubling new trend, according the cyber experts.
"They're quite literally holding your own data to ransom on your computer and demanding that you pay money to get access to your data once more," said James Lyne, global head of research at Sophos, a computer security firm.
A Los Angeles medical center hit last month paid $17,000 to get its system going again.
A short time later, similar attacks hit hospitals in Canada. The past few weeks have brought attacks on hospitals in Kentucky, West Virginia, and two more in Southern California.
James Trainor, the FBI's top cybercrime official says the problems is spreading.
"Last year, 2015, we saw a big uptick. And then the first quarter of 2016, very aggressive targeting of this critical sector," Trainor said. "In 2015 $24 million was paid out just in the ransom cost, and I think it's going up this year, unfortunately."
The FBI urges victims not to pay the ransom — advice many find hard to follow.