American and British spies hacked into the internal computer
network of the largest manufacturer of SIM cards in the world,
stealing encryption keys used to protect the privacy of cellphone
communications across the globe, according to top-secret documents
provided to The Intercept by National Security Agency
whistleblower Edward Snowden.
The hack was perpetrated by a joint unit consisting of operatives
from the NSA and its British counterpart Government Communications
Headquarters, or GCHQ. The breach, detailed in a secret 2010 GCHQ
document, gave the surveillance agencies the potential to secretly
monitor a large portion of the world’s cellular communications,
including both voice and data. […]
With these stolen encryption keys, intelligence agencies can
monitor mobile communications without seeking or receiving
approval from telecom companies and foreign governments.
Possessing the keys also sidesteps the need to get a warrant or a
wiretap, while leaving no trace on the wireless provider’s network
that the communications were intercepted. Bulk key theft
additionally enables the intelligence agencies to unlock any
previously encrypted communications they had already intercepted,
but did not yet have the ability to decrypt.
At this point we pretty much have to assume anything we do on a phone can be monitored.