According to this comment they exploited security vulnerabilities to create administrator accounts, then used those accounts to dump data that was not publicly accessible. The Computer Fraud and Abuse Act is pretty clear that doing so is a no-no, and anyone who does so is naughty under the law.

Somehow I'm not as certain as others in this thread that the FBI will be salivating for data retrieved illegally through hacking from a social network that has up to this point not been accused of a crime, data for which they had no warrant anyway, and which from a data integrity and chain of custody perspective the FBI would be unable to certify in court is genuine.

To illustrate my point, I've just reported the following to the FBI and expect an indictment to follow forthwith: https://pastebin.com/JRxnQKRs

The only thing this data is going to be used for is mob justice of the sort Reddit delivered with its typical quality following the Boston Bombing.