Government monitoring is done on massive scale.  As virtually all data communications goes through a limited number of communications centers around the nation and around the world.  Most communications centers have a separate room leased by the government.  Virtually all data coming into the center uses fiber-optic cable.  These fibers go through an optical splitter such that the one input gives two identical outputs.  One output continues to the communications center to be used as intended.  The second output goes to the government’s room.  This is passive monitoring as there is only a copy of the data sent.  No data is modified, and no indication is given on what is being monitored.

In the 1990s systems like the FBI’s Carnivore monitored email only and in a fairly rudimentary way.  New systems, Boeing’s NarusInsight have much greater capability.

Unencrypted data can be viewed in its entirety.  All standard email is available.  Just as modest cell phones can listen to our voice and interpret it as commands or text, advanced versions of the same software can transcribe all voice communications.  All phone traffic, the social call to a friend, the business call to a coworker, or the sensitive political or religious topic is easily transcribed and then process similarly to emails.  Conversations via chat services or websites provide the same text and user identification as email.

Encrypted data still contains useful information.  The source and destination IP addresses are unencrypted.  The time and size of the data are used for traffic analysis.  This information alone or even more when combined with unencrypted data can provide valuable information.