March 13 (Reuters) - UnitedHealth Group ( UNH ) said on

Wednesday its unit Change Healthcare's pharmacy network was back

online, weeks after a cyberattack had a knock-on effect across

the country's healthcare system that depends heavily on

insurance.

Change Healthcare processes about 50% of medical claims in

the United States for around 900,000 physicians, 33,000

pharmacies, 5,500 hospitals and 600 laboratories.

As of March 13, all major pharmacy and payment systems are

up and more than 99% of pre-incident claim volume is flowing,

UnitedHealth ( UNH ) said.

The company, however, added that its teams are working on

some pharmacies that are still offline.

Separately, UnitedHealth Group ( UNH ) said it has identified the

source of the intrusion and established a way to restore the

affected systems.

A thorough forensic analysis with Alphabet's

cybersecurity unit Mandiant and Palo Alto Networks is underway,

UnitedHealth ( UNH ) said, without providing additional details about

the source of the data breach.

Earlier in the day, the U.S. Department Of Health and Human

Services opened an investigation into the Feb. 21 cyberattack.

UnitedHealth ( UNH ) had blamed the hack on the "Blackcat" gang, a

notorious ransomware group that has a history of disruptive

attacks.

In a message posted to, and then quickly deleted from their

darknet site, the hackers said on Feb. 21 that they stole

millions of sensitive records, including medical insurance and

health data, from the company.

UnitedHealth ( UNH ) has also been hit with at least six class

action lawsuits accusing it of failing to protect millions of

people's personal data following the hack, with more lawsuits

likely to come.