WASHINGTON — Modern medicine in the Washington area reverted to 1960s-era paper systems when one of the largest hospital chains was crippled by a virus that shuttered its computers for patients and medical staff.

The FBI said it was investigating the paralyzing attack on MedStar Health Inc., which forced records systems offline, prevented patients from booking appointments, and left staff unable to check e-mail messages or even look up phone numbers.

The incident was the latest against U.S. medical providers, coming weeks after a California hospital paid ransom to free its infected systems using the bitcoin currency.

A law enforcement official, who declined to be identified because the person was not authorized to discuss an ongoing investigation, said the FBI was assessing whether a similar situation occurred at MedStar.

“We can't do anything at all. There's only one system we use, and now it's just paper,” said one MedStar employee who, like others, spoke on condition of anonymity because this person was not authorized to speak with reporters.

There were few signs of the attack's effects easing late Monday, with one employee at Georgetown University Hospital saying systems were still down, and saying some managers had to stay late and come in early because of the disruptions.

Company spokeswoman Ann Nickels said she couldn't say whether it was a ransomware attack. She said patient care was not affected, and hospitals were using a paper backup system.

But when asked whether hackers demanded payment, Nickles said, “I don't have an answer to that,” and referred to the company's statement.

MedStar operates 10 hospitals in Maryland and Washington, including the Georgetown hospital. It employs 30,000 staff and has 6,000 affiliated physicians.

Dr. Richard Alcorta, the medical director for Maryland's emergency medical services network, said he suspects it was a ransomware attack based on multiple ransomware attempts on individual hospitals in the state. Alcorta said he was unaware of any ransoms paid by Maryland hospitals or health care systems.

“People view this, I think, as a form of terrorism and are attempting to extort money by attempting to infect them with this type of virus,” he said.