Suspicious bitcoin-qt behaviour

[physalis]

Hi guys,

OK so I'm completely new to bitcoins, but I thought I had understood everything pretty well. Now I have seen some, as I think, very suspicious behaviour by my bitcoin-qt (v.0.7.2 beta).
I transferred 1 BC to my new address and tried out bitmillions.com. I send them exactly 0.13172332 BC.
Everything seemed to work fine, i could check my ticket, got what i won back and everything. Now the weird part is that later I tried to check the transaction at blockchain.info and saw this:

https://blockchain.info/tx/a31a76ea21bd5f25b9fa94a94228d3953624f67fd0de07b1ae73b2f251c4f091

It says that I emptied my whole wallet in that transaction, partly to bitmillions, but most of it going to some other address that I have not seen before.
In fact, when I check my balance now (on blockchain), there's nothing left except the return from bitmillions. In bitcoin-qt on my machine, everything looks OK, balance is fine.

Confused, I tried to reproduce that by transferring some BC to my different address on blockchain, made another transfer to bitmillions and got this, which looks fine to me:

https://blockchain.info/tx/a05241a0481e940012bfe7dca81bc4bbfb6bf19a8bda8db90be10a43d7daaf6d

Can someone explain this to me? Is that normal? If so, why the different behaviour?
Or is that in fact someone stealing from me?

Thanks in advance and excuse my bad english please

[1714700739]

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[1714700739]

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[1714700739]

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[physalis]

Ok, thank you.
So how would that work if I wanted to import my wallet to blockchain? If I import the private key, it doesn't know my true balance.

[Carmen]

I think this is a very good description of a change address.

https://bitcointalk.org/index.php?topic=140639.msg1497321#msg1497321

[physalis]

I think this is a very good description of a change address.

https://bitcointalk.org/index.php?topic=140639.msg1497321#msg1497321

It really is, thanks. I still don't really understand why bitcoin-qt has to create the 2nd address though, why not just use your own address as the 2nd output.
Blockchain seems to do it that way (Like here https://blockchain.info/tx/a05241a0481e940012bfe7dca81bc4bbfb6bf19a8bda8db90be10a43d7daaf6d).
Is that to make it harder to spy on other people's balances?

[grue]

I think this is a very good description of a change address.

https://bitcointalk.org/index.php?topic=140639.msg1497321#msg1497321

It really is, thanks. I still don't really understand why bitcoin-qt has to create the 2nd address though, why not just use your own address as the 2nd output.
Blockchain seems to do it that way (Like here https://blockchain.info/tx/a05241a0481e940012bfe7dca81bc4bbfb6bf19a8bda8db90be10a43d7daaf6d).
Is that to make it harder to spy on other people's balances?

yes, so it's not obvious you're sending to one address.

[deepceleron]

Noobs need to stop looking at websites to get misleading info, and just use the Bitcoin software.

[DannyHamilton]

So how would that work if I wanted to import my wallet to blockchain? If I import the private key, it doesn't know my true balance.

You could import the entire wallet into blockchain, and blockchain would take care of finding all the necessary private keys in the wallet.

If you wanted for some reason to import each private key individually, you'd have to acquire all the private keys from the wallet that has addresses associated with them.  Really though, unless you have a need to maintain the existing addresses in your wallet, you shouldn't need to import anything.You could just send all the bitcoins from Bitcoin-Qt to an address in your blockchain.info wallet if that was where you wanted the coins.