-UnitedHealth Group said on Thursday that the recent cyberattack at its tech unit, Change Healthcare, was perpetrated by hackers who identified themselves as the 'Blackcat' ransomware group.

The company said its experts were working with law enforcement authorities and third-party consultants to gauge the impact on its customers and patients.

The statement confirms a Reuters report on Monday. UnitedHealth had initially blamed a "suspected nation-state associated cybersecurity threat actor" for the disruption.

Blackcat has not returned repeated messages from Reuters, seeking a comment, including a message sent on Thursday asking about UnitedHealth's statement.

The problems began last week after hackers gained access to UnitedHealth's Change Healthcare unit, a vital lynchpin in the complex U.S. system for making and clearing insurance claims.

It affected electronic pharmacy refills and insurance transactions, particularly among independents, with some reverting to paper transactions.

  - Reuters