The National Security Agency is able to tap into most cellphone networks worldwide by discovering and taking advantage of security flaws that they discovered covertly. The extent of the operation – known within the agency as AURORAGOLD – was included in the documents provided to the website The Intercept by whistleblower Edward Snowden, and revealed for the first time this week.

In addition to spying on U.S. allies as well as its hostile countries, the operation planned to “introduce new flaws into communication systems so they can be tapped into,” The Intercept reported, calling it “a controversial tactic” as security experts say it means hackers may also be able to take advantage.

AURORAGOLD began with collection and analysis of messages sent among about 1,200 employees of various cellphone network operators worldwide. NSA agents intercepted strategy and planning document that enabled them to hack into the networks. The U.K.-based trade group GSM Association – ironically, funded by U.S. government to create technology to strengthen digital privacy – was among the operation’s targets.

The NSA is refuting the scope of AURORAGOLD, providing The Intercept with a statement that it is tracking “the communications of valid foreign targets” that pose threats to the U.S. or its allies. The NSA is permitted to do so under federal law.

Karsten Nohl, a cellphone security expert and cryptographer, told The Intercept that NSA was treading in dangerous territory by introducing “security vulnerabilities” into global communications systems. That kind of sabotage means that it would open the networks to hackers.