Revealed: how US and UK spy agencies defeat internet privacy and security

• NSA and GCHQ unlock encryption used to protect emails, banking and medical records • $250m-a-year US program works covertly with tech companies to insert weaknesses into products • Security experts say programs ‘undermine the fabric of the internet’ • Q&A: submit your questions for our privacy experts

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.