Washington, Sep 29 (IANS/RIA Novosti): US law enforcement surveillance of emails, text messages and phone calls are at an all-time high, according to government documents obtained by the American Civil Liberties Union.

"More people were subjected to pen register and trap-and-trace surveillance in the past two years than in the entire previous decade," wrote Naomi Gilens, a legal assistant with the ACLU's Speech, Privacy, and Technology Project, in an article on the ACLU's website.

Pen registers capture outgoing data, while trap and trace devices log incoming data, including information about the time and length of phone conversations, specific numbers called, and email addresses. While these types of surveillance devices are not used to capture phone conversations or to read the content of emails, the ACLU maintains the tools are "powerfully invasive".

"Twenty years ago, physical devices (were) attached to telephone lines in order to covertly record the incoming and outgoing numbers dialled," said Gilens. "Today, no special equipment is required to record this information, as interception capabilities are built into phone companies' call-routing hardware."

Between 2009 and 2011, data released by the Justice Department indicates the number of original orders issued for phone surveillance increased by 60 percent, according to the ACLU. And while it is still rare, data shows the number of authorisations to use surveillance devices on individuals' email and network data increased by 361 percent over the same two year span.

The US Justice Department says civil liberties of the general public were not infringed upon because it obtained court approval before using these types of surveillance devices.

"As criminals increasingly use new and more sophisticated technologies, the use of orders issued by a judge and explicitly authorized by Congress to obtain non-content information is essential for federal law enforcement officials to carry out their duty to protect the public and investigate violations of federal laws," said Justice Department spokesman Dean Boyd.

The ACLU says the legal standards that law enforcement agencies must meet before using these types of surveillance techniques are too low.

"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," Gilens wrote.

The ACLU is urging Congress to overhaul electronic surveillance laws and improve the reporting requirement so the public can have more insight into the government's use of wiretaps.