2. By extension, security-cracking in any other context (especially, but not exclusively, on communications networks).
At one time phreaking was a semi-respectable activity among hackers; there was a gentleman's agreement that phreaking as an intellectual game and a form of exploration was OK, but serious theft of services was taboo. There was significant crossover between the hacker community and the hard-core phone phreaks who ran semi-underground networks of their own through such media as the legendary "TAP Newsletter".
This ethos began to break down in the mid-1980s as wider dissemination of the techniques put them in the hands of less responsible phreaks. Around the same time, changes in the phone network made old-style technical ingenuity less effective as a way of hacking it, so phreaking came to depend more on overtly criminal acts such as stealing phone-card numbers.
The crimes and punishments of gangs like the "414 group" turned that game very ugly. A few old-time hackers still phreak casually just to keep their hand in, but most these days have hardly even heard of "blue boxes" or any of the other paraphernalia of the great phreaks of yore.