US and British intelligence agencies have successfully cracked much of the online encryption relied upon by hundreds of millions of people to protect the privacy of their personal data, online transactions and emails, according to top-secret documents revealed by former contractor Edward Snowden. The files show that the National Security Agency and its UK counterpart GCHQ have broadly compromised the guarantees that internet companies have given consumers to reassure them that their communications, online banking and medical records would be indecipherable to criminals or governments. The agencies, the documents reveal, have adopted a battery of methods in their systematic and ongoing assault on what they see as one of the biggest threats to their ability to access huge swathes of internet traffic - the use of ubiquitous encryption across the internet". Those methods include covert measures to ensure NSA control over setting of international encryption standards, the use of supercomputers to break encryption with "brute force", and - the most closely guarded secret of all - collaboration with technology companies and internet service providers themselves. Through these covert partnerships, the agencies have inserted secret vulnerabilities - known as backdoors or trapdoors - into commercial encryption software. "Backdoors are fundamentally in conflict with good security," said Christopher Soghoian, principal technologist and senior policy analyst at the American Civil Liberties Union. "Backdoors expose all users of a backdoored system, not just intelligence agency targets, to heightened risk of data compromise."