This words are from a very expert person who lives policing scams and fraudsters, so, as I think it's cool, maybe many of you can learn something:
"Here's what the scammer expects to happen, and invariably they are right.
You as the user, will put in a small amount - say 0.005 btc, and you will get your 0.01 btc back. Happy days, but you won't leave it at that. You will either put back the whole amount including profit, or just your profit - so you aren't losing anything right? OK so far, but at this point, you haven't gained either as you have put it back. Now, the scammer knows your wallet address, has not given anything away, and he will closely watch to see if he can get a higher amount out of you, and if not, you may still receive these little payments just for a while to instil trust - but it won't last.
What they want, is you to invite your friends and family to put into this great little earner, and some of them will put in everything they have. That's when the scam closes down and runs for the hills with all the bitcoin, the moment they have that big hit.
Just do the maths.
To pay double, they have to take in that much from somebody else, and then to double that persons coins, the same again - it soon reaches saturation point where they can't get enough new users to service the existing ones, and then they always stop paying out, and just take deposits in. All clear profit from stolen bitcoin.
Look at these numbers, and these don't take account of margin (were this intended to be legit)
1 user needs 1 more to deposit equivalent amounts so thats 1+1=2
Those 2 will no doubt redeposit so then it's 4, then 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, 8192 etc. In reality, it will only be in the tens or hundreds, or about 8-10 levels deep before it runs out of enough new investors. It is the fate of all Ponzi's."
Thanks buddy.
PS.: if this thread is in the wrong area, please admin, move it, because I think it will be helpful to many users. Thnks.