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

Wednesday that its unit Change Healthcare's pharmacy network was

back online, weeks after a cyberattack.

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, and the hack

had a knock-on effect across the country's healthcare system

which depends heavily on insurance.

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.

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.

The full extent of the data breach remains unknown, and the

company has previously said it was investigating.

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.