In the latest Snowden leak, Britain's electronic spying agency, in cooperation with the U.S. National Security Agency, hacked into the networks of a Dutch company to steal codes that allow both governments to eavesdrop on mobile phones.

The Intercept on Thursday detailed how the intelligence agencies employed the eavesdropping capability. According to the report, the two agencies targetted Netherlands-based Gemalto - the world's largest manufacturer of SIM cards, which are used by any mobile phone.

The Intercept offered no evidence of any eavesdropping against American customers of those providers, and company officials told the website they had no idea their networks had been penetrated, adding they would investigate a report

The NSA did not immediately respond to a request for comment.

The privacy of all mobile communications depends on an encrypted connection between the cellphone and the wireless carrier’s network, using keys stored on the SIM, a tiny chip smaller than a postage stamp, which is inserted into the phone. All mobile communications on the phone depend on the SIM, which stores and guards the encryption keys created by companies like Gemalto.So, under normal circumstances, when a mobile call, text, or other communication is made, that communication is encrypted as it travels through the air from a mobile device to a carrier’s tower. At that point, even if the communication was intercepted by a third party (like the NSA), it would be encrypted and indecipherable. But anyone who has obtained the encryption key for a particular wireless user could use it to decrypt that communication.

As the Intercept notes, "if an intelligence agency has been "passively" intercepting someone’s communications for a year and later acquires the permanent encryption key, it can go back and decrypt all of those communications."

This type of interception leaves "no trace on the wireless provider’s network" or on an individual users device.

In the past, former agency officials have defended using techniques to further surveillance capabilities, saying the U.S. needs to be able to eavesdrop on terrorists.