Security concerns when downloading the block chain from a 3rd party source?

It takes very long until bitcoin-core has downloaded the whole block chain. So I decided to download the block chain files via a bittorrent published by this website: http://www.getbitcoinblockchain.com

After the download was finished I noticed that the md5 checksums of the files from the torrent were different then of the files from bitcoin-core.

Why could that be?

Are there any security related concerns of using a block chain from a 3rd party source?

Can I retrieve missing Bitcoins that failed to process as Wallet is corrupt?

I have been using an old wallet until last year – Bitcoin Version v0.8.5-beta. QT Version 4.8.3.

I stopped using it as it has become corrupt. I had made several transactions that were not successful before I realized it was corrupt. They are showing in my transactions list as a question mark with 0 confirmations, however the transaction amount has been deducted from my wallet total.

I backed up the wallet.dat file after each transaction and overwrote the previous backup when I did this.

Can I retrieve the missing bitcoins?

Buy coins using a australian bank account from Germany

I am German living in Germany but do own an Australian bank account. I would like to use that money to buy bitcoins but somehow am not able to at the big exchange markets.
Whenever I identify myself it assignms me a German profile (which is fine) and only allows money transfer from european countries.

Is there a simple way to do this?
Sorry for this newbie question…

Where does the Bitcoin Core code serialize the number of transactions?

I’ve been studying the Bitcoin Core code, and I noticed that it uses a template READWRITE to serialize data structures for storing blocks. But it never seems to actually call “READWRITE(nTxs)”, the VARINT (CompactSize) that encodes the number of transactions. It reads the transactions to a vector (primitives/block.h), and it almost seems like it just magically knows how many txs there are. What gives?

Retrieve Bitcoin wallet details

We have a bitcoin wallet which we tried to update as it was dormantfor some 8 years plus but we were unable to do so as we haven’t got the Bitcoin wallet details.

Is there any way of retrieving my Bitcoin wallet details as we don’t have the wallet ID details.