WASHINGTON, March 5 (Reuters) - A website used by

hackers responsible for a breach at UnitedHealth Group ( UNH )

has been replaced by a notice saying it has been seized by

international law enforcement.

But at least one of the agencies allegedly responsible said

it had nothing to do with the seizure, raising the possibility

that the hackers - who also go by the moniker ALPHV - faked

their own takedown.

A message posted to the website of the Blackcat hacking

gang on Tuesday said it had been impounded "as part of a

coordinated law enforcement action" by U.S. authorities and

other law enforcement agencies. Among the logos of non-American

agencies involved were those of Europol and Britain's National

Crime Agency.

U.S. officials and Europol did not immediately return

messages seeking comment, but a National Crime Agency

spokesperson said: "I can confirm any recent disruption to ALPHV

infrastructure is not a result of NCA activity."

Several security experts said the takedown notice seemed

suspicious.

"This appears to be a classic exit scam," said researcher

Will Thomas. In an exit scam, some hackers pretend to be knocked

out of commission, only to quietly pocket their partners' money

and start over under a new name.

Thomas said Blackcat was already believed to be a

rebrand of a previous hacker group dubbed DarkSide.

"It would not be a surprise if they return once more in

the not-too-distant future," he said.

Even before the seizure notice, there were signs of

something unusual following the intrusion at the tech unit of

UnitedHealth ( UNH ), which has caused

serious disruption

across the United States.

Last week Blackcat posted a message saying it had stolen

millions of sensitive records from UnitedHealth ( UNH ), only to

delete the claim

without explanation.

On Sunday, someone posting to a hacker forum alleged

that the gang had cheated them out of their share of the

$22 million ransom

that UnitedHealth ( UNH ) had allegedly paid to restore its

systems.

UnitedHealth ( UNH ) had not commented on whether it paid a

ransom, and did not immediately return a message on Tuesday

seeking comment.