I was around during this time and can vouch for it. Back in the 90s there was really nothing like a computer security industry. Firewalls were things you heard about but almost never saw in practice. Systems were hooked up in ways which today would be considered gross negligence. University networks and Telenet were full of easily-accessible machines and networking equipment. One of the first times I got caught doing bad shit was on a SysV Unix system of the newspaper in the next town over. I had met another user on that system who was one of these vigilantes. He actually had caught me trying to root the box and deactivated my dialup login so that when I logged in, it spat out the motd and immediately disconnected. The message said to call a number for "support". I called the long distance number, and got questions and a lecture about my bad behavior. You know, being thirteen years old, I didn't think things through. I was just scared for my life that the cops were going to show up to my dad's house (they did later, for something different, but I digress). He was totally open about not working for the newspaper, and not being the regular sysop. He said he was another user trying to keep me from getting in real trouble.

There is a "telenet simulator" on the internet[0] that you should check out. This will give you some idea what it was like to use Sprint's Telenet system, which was a worldwide dialup network serving all kinds of juicy customers like banks, airlines, all kinds of businesses. This system had been devised and deployed long before the world wide web. Telenet had local dialups in most American cities[1]. Lots of those systems were using crap passwords, or defaults. You could use systems to dial other systems that weren't hooked into Telenet. It was tremendous fun exploring that network[2]. It was a hell of a lot of fun. Truly an exceptional time that I really have nostalgia for.

[0] http://telehack.com/

[1] http://textfiles.com/hacking/telnumbe.txt

[2] http://textfiles.com/hacking/telenet2.txt