The Washington Post reports the US National Security Agency is building a quantum computer to break the encryption that keeps data private worldwide.
The NSA project came to light in documents passed to the newspaper by Edward Snowden, a fugitive analyst now in Russia.
The BBC reports the agency hopes to harness the special qualities of quantum computers to speed up its code-cracking efforts.
The NSA is believed to have spent about $US80 million on the project but it is yet to produce a working machine.
However, the documents passed to the Post by Snowden suggest researchers are having some success developing the basic building blocks for the machine.