They are using a new type of network splicing, now, which might lead some to believe there is a flaw in the system. Clearly, law enforcement has been watching exit nodes and the cases that have gone forward where people have failed to repeatedly log in and out, making them easy to track. Other criminals have been caught via intercepted mail and with authorities even pretending to be sellers, or catching seller, then continue on using their contact channels. Thus far, I have not seen any prosecutions that indicate it is compromised, but there are a number of federal cases where they have dropped charges during discovery, where they were unwilling to reveal their methods of investigation. From what I can tell, nearly everything is compromised at a command and control level. Every device can be watched in real time, practically, and it isn't just the government doing the spying. In fact, most of the spying is done by and for marketing groups and is automated. This means no person is watching, but AI's are. Point being, using Tor is pointless if you haven't taken the steps to already lock down your devices and your network because they are constantly spouting your data. Provided you have taken those measures, the chances you are found and prosecuted based on your Tor activity are pretty slim. If they can do it, they aren't willing to reveal their secret, yet, to do a prosecution.