British spies helped the CIA find a way to convert 'smart' TVs into secret microphones using a codename inspired by Doctor Who killer monsters called 'Weeping Angels'.
MI5 worked with their US counterparts to develop software that convinced people their sets were switched off when in fact they were on and recording every word they say.
British spies have been central to developing the hack of TVs connected to the internet, according to WikiLeaks.
The spooks also chose to name it after Weeping Angels from Doctor Who - monsters who pretended to be stone statues before creeping up on unsuspecting victims.
US intelligence has also devised a method of remotely controlling cars and crashing them, leaked data claims.
Wikileaks sayst: 'The attack against Samsung smart TVs was developed in cooperation with the United Kingdom's MI5.
'After infestation, Weeping Angel places the target TV in a 'Fake-Off' mode, so that the owner falsely believes the TV is off when it is on. In 'Fake-Off' mode the TV operates as a bug, recording conversations in the room and sending them to a covert CIA server.'
WikiLeaks claimed the haul, which it dubbed Vault 7, Year Zero, exposed the agency's entire hacking tool kit, constituting an even bigger and more significant breach of US intelligence than the National Security Agency files leaked by analyst Edward Snowden.
The sensational revelation came after the website published 8,761 confidential US government files detailing CIA hacking and surveillance techniques.
Snowden's revelations showed the vast extent of routine electronic spying by the US and allies led by the UK.
Vault 7 concentrates on the ingenious ways they can do it, showing how the CIA steals data from targets and turns ordinary devices such as mobile phones, computers and internet-connected TVs into surveillance tools.
WikiLeaks claims the documents show that the spy agency can turn your TV into a listening device, bypass popular encryption apps, and possibly control your car.
The CIA refused to comment on the WikiLeaks haul but intelligence experts believe they are genuine.
Among the trove of secret files were the details of a joint US-UK operation called Weeping Angel, which discussed the tactics used to transform a F8000 TV for monitoring.
The document, which was marked secret and deals specifically with Samsung models, also had a 'USA/UK' label.
It says: 'Accomplishments during joint workshop with MI5/BTSS (British Security Service) (week of June 16, 2014).'
The file explains how to make a television appear to be switched off while it is used to spy on targets.
Referring to the British intelligence involvement, it detailed: 'Received sanitized source code from UK with comms and encryption removed.'
WikiLeaks, in a statement, said: 'The attack against Samsung smart TVs was developed in cooperation with the United Kingdom's MI5/BTSS. After infestation, Weeping Angel places the target TV in a 'Fake Off' mode, so that the owner falsely believes the TV is off when it is on.
'In 'Fake Off' mode the TV operates as a bug, recording conversations in the room and sending them over the internet to a covert CIA server.'
WikiLeaks claimed that a vast trove of CIA documents representing 'the majority of its hacking arsenal' had been leaked within the cyber security community and that it had received, and released, a part of them.
It said: 'This extraordinary collection, which amounts to more than several hundred million lines of code, gives its possessor the entire hacking capacity of the CIA.
'The archive appears to have been circulated among former US government hackers and contractors in an unauthorized manner, one of whom has provided WikiLeaks with portions of the archive.'
The website said the documents show the CIA has produced more than 1,000 malware systems, viruses, trojans, and other software that can infiltrate and take control of target electronics.
Former CIA operative and whistle-blower Edward Snowden, who is currently in exile in Russia, has tweeted that the claims by WikiLeaks were legitimate.
He posted: 'Still working through the publication, but what @Wikileaks has here is genuinely a big deal. Looks authentic.'
He added: 'If you're writing about the CIA/@Wikileaks story, here's the big deal: first public evidence USG(US government) secretly paying to keep US software unsafe.' He described this as 'reckless beyond words'.
While Julian Assange, the WikiLeaks editor-in-chief, said the documents show the 'extreme risk' of the uncontrolled spread of cyber weapons.
Mr Assange added: 'Comparisons can be drawn between the uncontrolled proliferation of such 'weapons', which results from the inability to contain them combined with their high market value, and the global arms trade.'
A spokesman for GCHQ said: 'We do not comment on intelligence matters'.
Samsung is 'urgently' investigating claims from WikiLeaks that intelligence agencies have used the firm's smart TVs as part of tools to spy on users.
The whistleblowing website has published thousands of documents it claims reveal the various hacking tools used by the CIA in the US, including techniques which target various consumer software, including Windows, Google's Android and Apple's iOS software.
The leaked report also claims software was developed to turn Samsung smart TVs into listening devices, a project codenamed Weeping Angel which the report claims also included input from the UK's MI5.
The Korean technology giant has now said it is investigating the claims made by WikiLeaks.
'Protecting consumers' privacy and the security of our devices is a top priority at Samsung,' the company said in a statement.
'We are aware of the report in question and are urgently looking into the matter.'
The leaked documents claim a 'fake-off' mode was created which tricked users into believing their TV screen was off when instead it was secretly recording audio that would be sent to CIA servers once the screen was turned back on and an internet connection re-established.
Many modern, internet-connected TVs come with voice control options, meaning a microphone is placed inside the device in order to pick up voice commands issued by users.
In 2015, Samsung warned users not to speak of 'personal or sensitive information' within listening distance of some its smart TVs as that information 'will be among the data captured and transmitted to a third party' after it emerged that, once activated, the voice control feature would 'listen' to what was being said and share it with Samsung or third parties.
1. MI5 and CIA develop smart TV hacking software and call it 'Weeping Angel' after the Dr Who monsters who pretend to be stone statues
2. Once installed the owner thinks it is off - but it is actually on, with a blank screen and standby red light on.
3. Unsuspecting victims will be unaware that their conversations are all now recorded
4. The software then sends back all the recording to the CIA's servers to be listened back