WikiLeaks has released what it describes as the largest ever publication of confidential documents on the United States' Central Intelligence Agency.
Code-named Vault 7, the first part comprises 8,761 documents called Year Zero, and said to come from an isolated, high-security network situated inside the CIA's Center for Cyber Intelligence in Langley, Virginia.
"This extraordinary collection, which amounts to more than several hundred million lines of code, gives its possessor the entire hacking capacity of the CIA," WikiLeaks said in a statement.
"The archive appears to have been circulated among former US government hackers and contractors in an unauthorised manner, one of whom has provided WikiLeaks with portions of the archive."
WikiLeaks claimed the documents include details of the CIA's global covert hacking tools, and dozens of "weaponised exploits" against a wide range of US and European company products, include Apple's iPhone, Google's Android, Microsoft's Windows and Samsung TVs, which are turned into "covert microphones".
Among the explosive claims made in the documents are that the CIA, in partnership with other US and foreign intelligence agencies, has been able to break the encryption on popular messaging apps such as WhatsApp, Telegram and Signal.
One cyber security consultant who had done work for the US government, who declined to be identified due to the sensitivity of the news, said the leak appeared to be legitimate.
US officials said they were unaware of where WikiLeaks might have obtained the alleged CIA material. One government source said he was unaware of any recent or current investigations into possible leaks of this kind of CIA material.
WikiLeaks founder Julian Assange, speaking from the Ecuadorian Embassy in London, said: "There is an extreme proliferation risk in the development of cyber 'weapons'.
"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.
"But the significance of Year Zero goes well beyond the choice between cyberwar and cyber-peace.
"The disclosure is also exceptional from a political, legal and forensic perspective."
Mr Assange has been living inside the embassy for more than four years after being granted political asylum.
He is wanted for questioning in Sweden over a sex allegation, which he denies, but faces extradition to the United States if he leaves the embassy.
"We do not comment on the authenticity or content of purported intelligence documents," CIA spokesman Jonathan Liu said in a statement.
WikiLeaks said it is rescheduling a planned press conference with Mr Assange because video stream links are "under attack".