https:// www.eff.org/deeplinks/2016/09/playpen-story-fbis-unprecedented-and-illegal-hacking-operation
>So how did the Playpen investigation unfold? The tip the FBI received pointed out that Playpen was misconfigured, and its actual IP address was publicly available and appeared to resolve to a location within the U.S. After some additional investigation, the FBI obtained a search warrant and seized the server hosting the site. But the FBI didn’t just shut it down. Instead, the FBI operated the site for nearly two weeks, allowing thousands of images of child pornography to be downloaded (a federal crime, which carries steep penalties). That decision, alone, has spurred serious debate.
>But it’s what happened next that could end up having a lasting impact on our digital rights.
>While the FBI was running Playpen, it began sending malware to visitors of the site, exploiting (we believe) a vulnerability in Firefox bundled in the Tor browser. The government, in an effort to downplay the intrusiveness of its technique, euphemistically calls the malware it used a “NIT”—short for “Network Investigative Technique.” The NIT copied certain identifying information from a user’s computer and sent it back to the FBI in Alexandria, Virginia. Over a thousand computers, located around the world, were searched in this way.