Believe it or not, there are still new revelations to be had regarding the various ways America’s National Security Agency spies on its targets. Just days before President Obama is expected to reveal a number of significant changes to the spying programs employed by the NSA, a new report from The New York Times sheds light on a previously unknown NSA spying tactic that allows the agency to conduct surveillance on computers that aren’t even connected to the Internet.

“While most of the software is inserted by gaining access to computer networks, the N.S.A. has increasingly made use of a secret technology that enables it to enter and alter data in computers even if they are not connected to the Internet, according to N.S.A. documents, computer experts and American officials,” The Times’ David Sanger and Thom Shanker wrote. “The technology, which the agency has used since at least 2008, relies on a covert channel of radio waves that can be transmitted from tiny circuit boards and USB cards inserted surreptitiously into the computers. In some cases, they are sent to a briefcase-size relay station that intelligence agencies can set up miles away from the target.”

According to the report, this method of spying is referred to by the NSA as an “active defense” and is used to thwart potential cyberattacks that might otherwise be perpetrated by foreign attackers. The Times says this tactic is used most often on computers belonging to various units in the Chinese Army, which has been accused on numerous occasions of being responsible for cyberattacks targeting American businesses and on the U.S. military.

While the methods employed by the NSA to spy on targets are becoming increasingly difficult to combat, there are some ways to thwart them. One such example is an upcoming device called the Blackphone, which is designed primarily to prevent snooping and other privacy breaches.