Thank you :) (you only need to share it now :p). Tracing back the transactions on the blockchain, the address used for proof of funds addr1 received the funds from addr2 which received them from addr3, These last two addresses are grayed out, I don't even know what it means ... Anyway I think that if you know your way around the blockchain you can make it very hard to trace a transaction. Concerning the legitimacy of the giveaway, some comments said that the user already gave 10 BTC (in some other giveaway) and everything seems to indicate that this is really true.