Playpen (website)

Playpen was a notorious darknet child pornography website that operated from August 2014 to March 2015. 
The website operated through a hidden service through the Tor network which allowed users to use the website anonymously. After running the website for 6 months, the website owner Steven W. Chase was captured by the FBI. After his capture, the FBI continued to run the website for another 13 days as part of "Operation Pacifier".
When it was shut down in March 2015, the site had over 215,000 users and hosted 23,000 sexually explicit images and videos of children as young as toddlers.
Website shutdown.
The shutdown operation, called Operation Pacifier, involved the FBI hijacking the site and continuing to serve content for two weeks (from February 19, 2015 until March 4, 2015). During this time the FBI used a malware-based "Network Investigative Technique" to hack into the web browsers of users accessing the site, thereby revealing their identities. The operation led to the arrest of 900 site users and three prison sentences.
While the FBI claimed to have knowledge about the existence of the website right from its beginning, it was unable to track down the servers locations or the site owner. The reason for their struggle was the fact that Playpen was hosted as a hidden service via Tor. Only a mishap of the site owner revealing his IP address finally allowed the law enforcement to track down both page and personnel.
Convictions.
The investigation led to the sentencing of Steven W. Chase, a 57-year-old from Florida who created the website, to 30 years in prison in May 2017. His two co-defendants pleaded guilty and were sentenced to 20 years each earlier in 2017 for their involvement in Playpen.
In 2017, charges were dropped against one member of the site, after the court demanded that details of the hacking tool be released. The FBI preferred to keep the NIT (network investigative technique) malware a secret for future investigations.
Shutdown criticisms.
The investigation was criticized by the Electronic Frontier Foundation because, after having taken control of the website, the FBI continued for nearly two weeks to operate the website and thus distribute child pornography, i.e. exactly the same crime the bureau sought to stop. The lawyer of a defendant in the case stated that the FBI not only operated the website, but improved it so its number of visitors rose sharply while it was under their control. 
The Head of the European Cybercrime Centre Steven Wilson defended the actions of the FBI stating that "If we operate with 19th century legal principles then we are unable to effectively tackle crime at the highest level." and "We need to balance the rights of victims versus the right to privacy".
Challenges were raised about the FBI's possibly severe misuse of the initial search warrant, leading to the likely dismissal of much of the gathered evidence against one defendant. On August 28, 2019, the Eleventh Circuit Court of Appeals ruled that the warrant was invalid but that the evidence obtained was not required to be excluded due to the good-faith exception doctrine.