
Once a hacker gets to know a loophole in a system that no one else knows about, it is called a zero-day exploit. Suppose I found a vulnerability in google chrome which no one knows about, it is marked as zero-day exploit. Instead of giving the exploit to google for patching it up, I would sell it to some other guy for a larger amount. This is where black hats mainly get money from.
Fox’s book is a little outdated now, but the alternative passive income streams he mentions includes straight up blogging (with the advertising and affiliate marketing as the natural monetization strategy), but also podcasting (don’t agree with this so much as a direct revenue stream) and vlogging (video blogging / web TV, whatever you want to call it).


We suppose you already know that you can find so much online ways to earn money from your computer. Some of the ways are cool and easy, the others are a bit boring but at the end of the day, you still get cash for simple stuff! So, today we’ll present you the ways to make money by chatting online. You must be confused, right? We all do it daily for no money, why would that be paid? You’ll see how to do it in the text below!

Go to a chat or video-chat website that will pay you for each per-click action made from their members. Click the "Sign Up" button and complete the required information on the application form. Make certain you have a valid government-issued picture ID, such as your driver's license or passport. You'll also need a webcam or compatible video camera recorder when you're signing up with a video-chat service.
While the “get paid to chat” jobs often serve students from Asia, Cambly seems to draw from an even wider geographical base. In addition to Asia, it has students from South America, Saudi Arabia, India, Turkey, South Korea and others. It seems like a good way to get paid to share your language and culture while learning a lot about other cultures too.
In regard to sources of income, it is not necessarily coming from Blackhat activities, White hat work might fund hacktivism. Some are students supported by family, some have mundane side jobs. Some get paid for their technical skills in regular IT jobs, some speak at info-sec conferences, write articles and books, do consultancy or do work as paid media sources. 

You’ll also have to decide whether or not to make your ebook exclusive to Amazon Kindle through their KDP Select program. I’ve done it temporarily (you enroll for 90 days at a time), and there are some advantages, like special promotional and pricing opportunities. But eventually, you might like to offer your book through other channels (more on this below).

On a simpler side, I once knew a hacker who got through many of his college years by loading gift cards to stores and restaurants with artificial value. Pretty much programming the gift cards so that they seemed to be loaded with a considerable out of money and using them. He eventually got caught, but you can leave that part out of your book.  ;-)
Black market import/export - this is Breaking Bad’esqe but my understanding is that it definitely happens. Making high quality Methamphetamine - Wikipedia requires precursors that are tightly controlled in the US but not so much in developing countries. So basically you find some meth cooks, offer to sell them this stuff, and setup a “real looking” entity to buy it. Very illegal.
Contrary to authors’ fantasies, books don’t sell themselves. It is true that ebooks are easier to get in front of potential buyers than print books, but I consider myself lucky to have made decent money and to still have Kindle income every month (even if it was only $104 last month). To really hit it big, you need to learn about marketing, which is beyond the scope of this article (and mostly beyond my skills, which explains the $104). Fortunately, there is a lot of good information about marketing Kindle books online.

Hack for hire is possible, selling their 'hacking' skills as a service. However this will only work for a limited minority with the right connections as well as well as the right skills. Discovering and selling exploits and root kits is possible, selling pirate software, music and DVDs. There are grey activities such or bounty hunting exploits or Botnets for game gold farming, against T&C but not criminal law.