In the early 1990s a friend of mine ran a dial-up BBS. It was completely unmoderated (aside from spam), and ended up become a rather active board for (mostly black hat) hackers to post and trade information. My friend wasn't involved in any hacking directly - he simply ran the BBS which also hosted a bunch of doors (games) like TW2002 that were also quite popular. One day, a mutual friend of ours (who was an aspiring black hat hacker) got picked up by the FBI for a variety of phone phreaking offenses. During questioning, they asked him a bunch of questions about the BBS. As soon as he got out on bail, he relayed this information to my friend who ran the BBS. Needless to say, the BBS was shut down and all of the disks/hard drives trashed within an hour.

Thankfully there were never any legal implications for my friend with the BBS, but you can be damn sure there were quite a few sleepless nights subsequently as he waited for a knock on the door!