Three legal advocacy organizations have published a new guide for criminal defense attorneys who are defending more than 200 people who are accused of accessing Playpen, a now-shuttered notorious child porn site that was only available as a Tor-hidden service.

The Playpen prosecutions, which are unfolding nationwide, have raised significant questions as to what the limits of government surveillance should be—and how much judicial and legislative oversight exists for authorized government hacking.

In order to find the suspects, federal authorities seized and operated the site for 13 days before closing it down in 2015. During that period, the FBI deployed a Tor exploit that allowed them to find out those users’ real IP addresses. The use of Tor, which obscures and anonymizes IP addresses and browser user agents, makes it significantly more difficult for individuals to be tracked online. With the exploit, it became extremely easy for suspects to be identified and located. The Department of Justice has called this exploit a "network investigative technique," (NIT) while many security experts have dubbed it as "malware."

The new 48-page guide—authored by the Electronic Frontier Foundation, the American Civil Liberties Union, and the National Association of Criminal Defense Lawyers—seeks to:

…educate defense attorneys about these highly intrusive surveillance techniques and to help them prepare a zealous defense on behalf of their clients against secretive and potentially unlawful hacking. Such hacking has never been discussed by Congress, and we in no way endorse government hacking. However, given that the federal government is deploying malware and a recent amendment to Rule 41 only makes such deployment easier, it is our goal to ensure that all uses of malware are subject to meaningful Fourth Amendment analysis so that malware is installed only when supported by individualized suspicion. Our Fourth Amendment right to be free from unreasonable searches applies regardless of whether new technology is involved in effectuating a particular search; however, the law may be slow to catch up, particularly when the government goes to great lengths to hide details about its use of new surveillance techniques.

The Rule 41 line refers to a recent controversial revision to the federal rules of criminal procedure that took effect on December 1, 2016. The change now allows a lower-level federal judge, known as a magistrate, to sign off on a warrant authorizing the use of a NIT anywhere in the country. Previously, magistrates could only authorize a NIT within the limited federal judicial district that they oversee.

“Level the playing field”

According to Colin Fieman, a federal public defender based in Tacoma, Washington, who has represented two Playpen defendants, the new guide is "timely and invaluable."

"For too long the government has used secrecy and misinformation to extend its hacking powers without adequate oversight, and the guide does a great job of explaining how defense attorneys, and the public at large, can protect our shared privacy interests and constitutional rights in an increasingly Orwellian world of mass hacking," he e-mailed Ars.

Earlier this month, prosecutors dropped a case against one of Fieman’s clients, Jay Michaud, rather than disclose the now-classified NIT source code.

Meanwhile, Orin Kerr, a law professor at George Washington University and one of the nation’s top computer crime scholars, said that the 188-page primer was "very useful," and would "help level the playing field in the courts of appeal."

"The Playpen warrant cases are unusual in that there are so many cases around the country, all effectively identical, working their way up to the courts of appeals," he e-mailed Ars. "DOJ is coordinating its briefs, and that coordination helps the government put its best arguments forward. There is naturally less coordination on the defense side. The lawyers on the defense side have fewer opportunities to get up to speed on both the technology and the law. This guide can help the different defense lawyers get up to speed. Of course, that's not to say I agree with the arguments in the guide. But evaluated as a work designed to help advocates, I think it's useful."