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.

In 2001, the DoJ issued only 5,683 reported "original orders." (.pdf) Fast forward to 2011, the latest year for which data is available, the number skyrocketed to 37,616 – a more than sixfold increase. Though these can be used to track e-mail, the vast majority are used to get information on mobile phone users' phone calls and texts.

According to the ACLU:

Because these surveillance powers are not used to capture telephone conversations or the bodies of emails, they are classified as 'non-content' surveillance tools, as opposed to tools that collect 'content,' like wiretaps. This means that the legal standard that law enforcement agencies must meet before using pen registers is lower than it is for wiretaps and other content-collecting technology. Specifically, in order to wiretap an American’s phone, the government must convince a judge that it has sufficient probable cause and that the wiretap is essential to an investigation. But for a pen register, the government need only submit certification to a court stating that it seeks information relevant to an ongoing criminal investigation. As long as it completes this simple procedural requirement, the government may proceed with pen register or trap and trace surveillance, without any judge considering the merits of the request.

Even more alarming, the latest figures – which were for years 2010 and 2011 – open only a tiny window into the U.S. surveillance society.

Consider that last year mobile carriers responded to a staggering 1.3 million law enforcement requests – which come from federal, state and local police, as well as from administrative offices – for subscriber information, including text messages and phone location data. That's according to data provided to Congress that was released in July.

The nation's major phone providers said they were working around the clock and charging millions in fees to keep up with ever-growing demands.

AT&T, the nation’s second-largest mobile carrier, told Congress that it had received 63,100 subpoenas – no judicial oversight required – for customer information in 2007. That more than doubled to 131,400 last year. By contrast, AT&T reported 36,900 court orders for subscriber data in 2007. That number grew to 49,700 court orders last year, a weak growth rate compared to the doubling of subpoenas in the same period.

Not surprisingly, the number of people affected by such orders has jumped as well - consider the below chart on the number of people who the DoJ got information about using trap-and-traces and pen registers.

All of this only concerns disclosed monitoring. The Electronic Frontier Foundation, in ongoing litigation, claims the National Security Agency, with the help of the nation's telecoms, is hijacking all electronic communications.

The Justice Department, meanwhile, filed the latest pen register and trap-and-trace reports for 2010 and 2011 with Congress, which the law requires. But the Justice Department refused to release the numbers publicly and did so only after the ACLU sued.