The Justice Department use of warrantless internet and telephone surveillance methods known as pen register and trap-and-trace has exploded in the last decade, according to government documents the American Civil Liberties obtained via a Freedom of Information Act claim.
Pen registers obtain, in real time, non-content information of outbound telephone and internet communications, such as phone numbers dialed, and the sender and recipient (and sometimes subject line) of an e-mail message. A trap-and-trace acquires the same information, but for inbound communications to a target. No probable-cause warrant is needed to obtain the data. Judges are required to sign off on these orders when the authorities say the information is relevant to an investigation.

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