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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.

I found something interesting and I'd like to share it!
This address contained little over 1000 BTC since 2013-07-10
https://blockchain.info/address/13tikBdmMVkyuykDVNmv3tTr8YkVN3Xrut
and he sends the coins to
https://blockchain.info/address/1Hy1rceh2EaKnAQhGZocTFUGnKFFD3mNG5
on 30th July 2016 who again sends the coins to
https://blockchain.info/address/1BfxSuxJqXuizBbTcP238JZY9DT4eqvzJG
on 3rd August, 2016. If I'm not wrong Bitfinex was hacked about 2 days ago i.e. on 2nd August!
Even if we consider that Bitfinex was hacked on 30th July the funds were in that wallet since 2013 and havent been moved until now which clearly indicates that he's lying about the source of that money. It could be stolen money from MTGox though, just a hunch.

Oh! I didn't notice the dates of the transactions, nice find ;).
Technically rekcahxfb didn't say anything about the source of the funds. They just said

reverse my name

which implies they are the author of the Bitfinex hack, maybe that is not true ... rekcahxfb is apparently using funds which do not come directly from the stolen funds, this is not contradictory with them being the hacker.

Thanks!
You have a valid point too. Let's wait for the outcome.
Just hoping that whoever wins, returns the money back to the owners.(if rekcahxfb keeps his promise)

Nice detective work guys. Crazy times.

I saw the grayed out Address, it's because the address sending the funds is also used to receive the change.
Grayed Out

Source

It looks difficult to trace back but I'm still gonna try now.

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