AMSTERDAM, Aug 13 (Reuters) - A prolific hacking group known

for exploiting software vulnerabilities to attack multiple

targets simultaneously claimed it had stolen large volumes of

data from nearly 50 companies worldwide, including Philips

, Shell, Fiserv ( FISV ) and GE,

according to a posting on the group's website.

Philips said it had been targeted by Cl0p while Shell said

it was aware of a recent "possible incident", confirming an

earlier report on Thursday by Dutch media outlet BNR.

"We are working with our security teams and relevant experts

to investigate the situation," a Shell spokesperson said.

"Philips has identified and contained an attempted

cybersecurity compromise of a specific enterprise server related

to internal data," Philips said in a statement, adding that the

incident does not impact customer environments.

A spokesperson for Fiserv ( FISV ) said the company is aware of the

threat actor's claims, but "based on our comprehensive review to

date", it had found no evidence that customer, banking,

transaction or personal data had been compromised, or that its

operating environment had been affected.

GE could not immediately be reached for comment.

Reuters could not independently verify the hacking group's

claims regarding the kind of data it stole and how much. The

hackers did not respond to a request for comment.

While it's not clear how the hackers allegedly accessed the

companies, Ransom-ISAC, an industry information sharing group,

issued a notice July 22 warning that the hacking group was

exploiting vulnerabilities in PTC Windchill and FlexPLM,

software used to aid in engineering and manufacturing

processes.

Boston-based PTC did not immediately respond to a request

for comment. The company has issued multiple security notices to

its website, dating to June 18, urging customers to apply a

patch for a vulnerability and sharing details about an unnamed

attacker attacking its products.

Brandon Parsons, threat intelligence manager with Ascent

Solutions and the author of the Ransom-ISAC advisory, said some

companies began receiving notices from Cl0p on July 19 or July

20. The group focuses on vulnerabilities in key software

packages rather than specific companies, he said, calling them

"professional data extortionists."

"They don't really target a specific company, they target a

specific zero day vulnerability and go after it," Parsons said,

referring to previously unknown bugs that software vendors

haven't yet issued patches for.