fake twitter followers

Check it out for yourself, I've lost around 100 followers on a 15k+ follower account of what I thought were all real followers. After seeing that, I then went and checked my other accounts and lost 10's of thousands.. I didn't buy from the same people so I know it isn't just that, and it isn't...

I'm quite curious to know that how fake followers are created and how does this all work(including the fiverr gigs which are like "I will add 35,000 real looking twitter followers to your account in less than 24 hours for $5 ? Also are there any beginners guide or some learning resource...