The American National Security Agency (NSA) is collecting almost 200 million text messages a day from around the world, and used the data to extract details such as location, contact networks and credit card details.
What's more, the UK's own Government Communications Headquarters (GCHQ) have had access to that information, and have searched for the details of British telephone users.
The revelations have appeared as part of the treasure trove of documents released by whistleblower Edward Snowden in June of last year.
An agency presentation from 2011 reveals how a program codenamed "Dishfire" collected an average of 194 million text messages a day in April 2011. It is unknown how the agency's snooping has expanded since then, although it's fair to say that it probably hasn't shrunk in the intervening years.
In addition to storing the messages themselves, a further program known as "Prefer" conducted automated analysis on the untargeted communications.
The presentation slide is subtitled "SMS Text Messages: A Goldmine to Exploit."
The NSA has told reporters that the programme stored "lawfully collected SMS data".
"The implication that NSA's collection is arbitrary and unconstrained is false," the NSA said.
A second slide shows how the metadata led the agency to collect a whole portfolio of other invasive information about the targeted phone users.
The NSA was able to collect data on missed calls, SIM card changes, passwords, flight plans, financial transactions and even when and how often a surveillance target crossed international borders.
The release comes just as President Obama prepares to give his verdict on reform of the spy organisation, which privacy groups have criticised for vastly overreaching its remit to protect the United States.