Documents released today as a result of the House v. Napolitano settlement document the systematic use of laptop searches at the US border to evade the need to get a warrant to read Americans' email. They way it worked: Homeland Security Investigations has someone they want the goods on, but don't think a judge would grant them a warrant. They put their victim on a travel advisory list, and the next time she crosses the border, the CBP seizes her laptop and phone and whatever other devices she's carrying and they get a copy of all of her data: no warrant required. They used this trick to seize the documents of David House, who worked to raise money and public support for Chelsea Manning (formerly Bradley Manning), and eventually had to settle a lawsuit brought by House and the ACLU, a condition of which was the release of these documents.
The settlement documents reveal that an agent with Homeland Security Investigations (HSI)—an Immigration and Customs Enforcement (ICE) subdivision that is now the second largest law enforcement agency in the United States—entered a "lookout" into a government database called TECS (see the document here), effectively notifying government agents throughout the country that House was wanted for questioning in connection with the Department of Justice's investigation into Manning and WikiLeaks. As a result of the lookout, which was linked to the Advance Passenger Information System, HSI later received an automated notification that House would be traveling outside the country and that he would return through O'Hare on November 3, 2010…
…Unfortunately, House's case is not an isolated incident. The government's own records indicate that 4,957 passengers had their electronic devices searched between October 1, 2012 and August 31, 2013, and an additional 4,898 individuals were subject to electronic device searches the previous year.