The German news magazine said the worker was now employed by Siemens in Munich.

"We take this seriously and we are looking into this. We cannot reveal any information about the identity of the person due to data protection laws," Siemens said on Friday.

Der Spiegel reported on Friday that more than 90 former staff from NTC Vulkan worked for a several other European companies.

The magazine said NTC Vulkan maintains close ties to all three major Russian intelligence services: FSB, GRU and SWR.

Its so-called "Vulkan Files" said the company builds cyber programmes for the security services aimed at attacking critical infrastructure facilities.

NTC Vulkan did not respond to requests for comment.

An ex-chief developer of the company is working as a "senior software development engineer" at Amazon Web Services (AWS) in Dublin, Der Spiegel also reported. Amazon did not respond to a request for comment.

(Reporting by John Revill#; Additional reporting by Hakan Ersen; Editing by Mark Potter)