What if some dark hacker makes a bot to create fb accounts,emails and simulates autoclicks?
Then all this becomes injustice, he could get hundred of thousands stellars
It won't work, newly created fb accounts are not eligible to get free stellars. The facebook account must have some friends, photos, and should not be new.
Also should be phone verified. facebook has really strict restrictions about it's phone verification.
You are right at some point, but look at that: a guy (everettworth) who has already collected 2 million stellars using "fake" accounts.
Here's an article (in russian):
http://xakep.ru/news/stellars-mechanical-turk/In common it's about he was using Amazon Mechanical Turk service to do that by
placing a task and reward for completing it.
The task was quite simple:
1. register on stellar.org;
2. verify your unique account via facebook;
3. get 6000 stellars and send them to his adress.
The reward for completing the task was 1-2$ which means he paid for it approximately from 343$ to 685$. And now 2m stellars value is 4230$, so he made profit
Tell me where to send em ... =) 
