MedStar Health says 90 percent of its computer systems are back online after it fell victim to a crippling attack that encrypted data this week.
Inpatient and outpatient health records systems were up and running Friday, as were registration and scheduling systems, MedStar said in a statement.
The health system, which operates 10 hospitals and other facilities in the region, said it gave priority in its recovery efforts to fixing computer systems used for patient care and is now turning to resolve other problems.
MedStar reported the problems, which it has described as a computer virus, on Monday. Technical teams pulled systems offline to stop the infection from spreading, the company said, leaving clinicians to rely on paper records to track patients.
The hospital network is the latest high-profile victim of a type of attack known as ransomware, in which hackers demand payment in exchange for keys to regain access to data that they have encrypted.
The hackers who targeted MedStar sought the equivalent of $18,500 in the digital currency bitcoin, according to a ransom note obtained by The Baltimore Sun.
MedStar has stressed that no patient data was compromised, but it is not clear whether it has been able to recover any information that was encrypted.
While some doctors and nurses have reported working more slowly without the benefit of electronic records, MedStar says it has continued to see patients at close to normal volumes.