Nato is assessing the impact of a data breach of classified military documents being sold by a hacker group online, BBC reports.
The data includes blueprints of weapons being used by Nato allies in the Ukraine conflict.
Criminal hackers are selling the dossiers after stealing data linked to a major European weapons maker.
MBDA Missile Systems admitted its data was among the stash but claimed none of the classified files belong to the firm.
The pan-European company, which is headquartered in France, said its information was hacked from a compromised external hard drive, adding that it was cooperating with authorities in Italy, where the data breach took place.
It is understood investigations are centred around one of MBDA`s suppliers.
In a statement, a Nato spokesperson said: "We are assessing claims relating to data allegedly stolen from MBDA. We have no indication that any Nato network has been compromised."
Cyber criminals, operating on Russian and English forums, are selling 80GB of the stolen data for 15 Bitcoin (approximately £18,000) and claimed to have sold the stash to at least one unknown buyer so far.
In their advert for the stolen data, the hackers claimed to have "classified information about employees of companies that took part in the development of closed military projects" as well as "design documentation, drawings, presentations, video and photo materials, contract agreements and correspondence with other companies".
A free 50MB sample of the data, seen by the BBC, includes documents labelled "NATO CONFIDENTIAL", "NATO RESTRICTED" and "Unclassified Controlled Information".
In addition to the sample, the criminals supplied additional documents by email, including two marked "NATO SECRET".
