WASHINGTON, April 9 (Reuters) - A freshly formed hacking

gang claims to have won access to a massive stash of data stolen

from UnitedHealth Group ( UNH ), the largest U.S. health

insurer, but with little evidence to go on it is not clear

whether they are telling the truth.

Hackers walloped UnitedHealth ( UNH ) in February, paralyzing

billions of dollars worth of health insurance payments across

the country. The ransomware gang "Blackcat" initially said on

its website that it had stolen 8 terabytes of sensitive records

- including medical insurance and health data - only to swiftly

delete the statement without explanation.

The new group, "Ransomhub," told Reuters that a disgruntled

affiliate of Blackcat gave the data to them after a botched

ransomware payment allowed Blackcat's hackers to vanish with $22

million in bitcoin.

Ransomhub refused to provide any backing for their claim or

identify the affiliate.

"We will not disclose any information," the hackers said in

a chat.

UnitedHealth ( UNH ) said it was aware of the claim and was

continuing to work with authorities. The FBI did not immediately

return a message.

UnitedHealth ( UNH ) has stayed mum on whether it paid the

cybercriminals, but a hacker forum posting - backed by forensic

blockchain evidence - claimed that Blackcat had cheated an

affiliated hacker or hacker group out of a $22 million ransom

paid by UnitedHealth ( UNH ) to help contain the breach.

Blackcat then pulled a disappearing act, falsely claiming to

have been nabbed by law enforcement.

Ransomhub told Reuters the Blackcat affiliate has since

handed the data to them for resale. It declined to answer

further questions, saying the group was busy.

With so much intrigue already surrounding the hack, experts

urged caution about the claim.

Analyst Brett Callow of cybersecurity company Emsisoft said

he suspected Ransomhub's claim was true, but he cautioned that

he was making "a very low confidence guess" and that the group

could be trying out a scam.

Darren Williams, the chief executive of cybersecurity

company BlackFog, said he had seen a couple of gangs recently

try to boost their credibility by lying about what they had. He

said the latest claim was "highly likely" a bluff.