Hello ? Any help ?

My friend told me about x2coin.byethost5.com yesterday, I tried it and was very happy. But when I tried to double my btc second time they did not do it. I even tried a different btc address from a different pc (different ip address) with no success. Not that I am very greedy, but I just want to understand how they know that someone doubled before already. My friend also had no success second time, though it worked the first time for both of us. Also, how do they manage to giveaway so many bitcoins? is it all donations or do they mine like freebitco.in does ?