Cyber extortionists have stolen sensitive data from a company which supports the US Minuteman III nuclear deterrent.

Hackers have stolen confidential documents from a US military contractor which provides critical support for the country’s Minuteman III nuclear deterrent, Sky News has learnt.

After gaining access to Westech International’s computer network, the criminals encrypted the company’s machines and began to leak documents online to pressure the company to pay extortion.

It is unclear if the documents stolen by the criminals include military classified information, but files which have already been leaked online suggest the hackers had access to extremely sensitive data, including payroll and emails.

There are also concerns that Russian-speaking operators behind the attack could attempt to monetise their haul by selling information about the nuclear deterrent on to a hostile state.

Court documents in the US allege that Russian cyber criminals with a financial motivation have collaborated with the intelligence services in order to steal classified government documents.

A spokesperson for Westech confirmed to Sky News that the company had been hacked and its computers encrypted, and that investigations to identify what data the criminals had managed to steal were ongoing.

The company is involved with the nuclear deterrent as a sub-contractor for Northrup Grumman, providing engineering and maintenance support for the Minuteman III intercontinental ballistic missiles.

Minuteman III is the land-based component of the US nuclear deterrent, stored in hundreds of protected underground launch facilities operated by the US Air Force.

Each ICBM is capable of delivering multiple thermonuclear warheads further than 6,000 miles, or the distance between London and Buenos Aires.

Brett Callow, a researcher for Emsisoft which specialises in tackling ransomware incidents, told Sky News: “This is not the first incident in which a contractor has leaked data and, unless action is taken, it will not be the last.

“The information exposed in these incidents could potentially be of interest to other nation states and present a risk to both national security and to the safety of service personnel.

“Even if a company pays the ransom, there is no guarantee that the criminals will destroy the stolen data, especially if it has a high market value.

“They may still sell it to other governments or trade it with other criminal enterprises,” Mr Callow warned, adding that another criminal group operating under the same model is offering interested parties the opportunity to bid for its stolen data.

Westech’s computers were encrypted with the MAZE ransomware, which is traded on a range of Russian-speaking underground cyber crime markets and has been used to attack dozens of companies in the West in the past year alone.

The creators of MAZE seem to operate under an affiliate model allowing hackers to use their tool in exchange for a slice of the profits, according to research into the group by cyber security firm FireEye.

Charles Carmakal of FireEye’s incident response arm Mandiant told Sky News that the creators of the ransomware were definitely separate from the groups operating it – although there was some co-ordination between them all.

The creators have a centralised voice through their naming and shaming website, Mr Carmakal noted, where they leak documents in order to extort their victims.

However there are various groups performing the attacks themselves, some of whom FireEye has identified recruiting collaborators on Russian-language cyber crime forums.

Mr Carmakal said it was not always easy for these types of criminals to get access to their governments if they wished to sell particularly valuable data.

“The real risk is that, as these groups have proven they will do, the threat actors will publish the data they’ve stolen,” he added.

Westech’s spokesperson told Sky News: “We recently experienced a ransomware incident, which affected some of our systems and encrypted some of our files.

“Upon learning of the issue, we immediately commenced an investigation and contained our systems,” they added.

“We have also been working closely with an independent computer forensic firm to analyse our systems for any compromise and to determine if any personal information is at risk.”

Sky News can confirm that personal information is included in the documents which the criminals have leaked online.

Northrup Grumman and the US Department of Defense declined to comment.