MANCHESTER, Conn. (AP) — Key computer systems at hospitals and clinics in several states have yet to come back online more than two weeks after a cyberattack that forced some emergency room shutdowns and ambulance diversions.

Progress is being made “to recover critical systems and restore their integrity,” Prospect Medical Holdings said in a Friday statement. But the company, which runs 16 hospitals and dozens of other medical facilities in California, Connecticut, Pennsylvania, Rhode Island and Texas, could not say when operations might return to normal.

“We do not yet have a definitive timeline for how long it will be before all of our systems are restored,” spokeswoman Nina Kruse said in a text message. “The forensic investigation is still underway and we are working closely with law enforcement officials.”

The recovery process can often take weeks, with hospitals in the meantime reverting to paper systems and people to monitor equipment, run records between departments and do other tasks usually handled electronically, John Riggi, the American Hospital Association’s national advisor for cybersecurity and risk, said at the time of the breach.

The attack, which was announced Aug. 3, had all the hallmarks of extortive ransomware but officials would neither confirm nor deny this. In such attacks, criminals steal sensitive data from targeted networks, activate encryption malware that paralyzes them and demand ransoms.

The FBI advises victims not to pay ransoms as there is no guarantee the stolen data won’t eventually be sold on dark web criminal forums. Paying ransoms also encourages the criminals and finances attacks, Riggi said.

As a result of the attack, some elective surgeries, outpatient appointments, blood drives and other services are still postponed.

Eastern Connecticut Health Network, which includes Rockville General and Manchester Memorial hospitals as well as a number of clinics and primary care providers, was running Friday on a temporary phone system.

Waterbury Hospital has been using paper records in place of computer files since the attack but is no longer diverting trauma and stroke patients to other facilities, spokeswoman Lauresha Xhihani told the Republican-American newspaper.

“PMH physicians, nurses, and staff are trained to provide care when our electronic systems are not available,” Kruse wrote. “Delivering safe, quality care is our most important priority.”

Globally, the health care industry was the hardest-hit by cyberattacks in the year ending in March, according to IBM’s annual report on data breaches. For the 13th straight year it reported the most expensive breaches, averaging $11 million each. Next was the financial sector at $5.9 million.

Health care providers are a common target for criminal extortionists because they have sensitive patient data, including histories, payment information, and even critical research data, Riggi said.