Bitcoin Forum

I think someone managed to leech a good chunk of my bitcoin.  I sent a transaction of less than two bitcoin, but it somehow got coupled with a transaction of 107 bitcoin to an unknown address.  In panic, I tried to move all my bitcoin to a new address.  That transaction went through, but then another transaction was sent to the same address and an unknown address.

I used to use the blockchain e-wallet, but that seemed to be having trouble today, so I made an electrum wallet.  I know that wasn't a good idea, since my system isn't secure, but any idea what could have happened?

LOL

Man, that unknow address is YOURS! It's the change address. You still see the Bitcoins available to spend on your client, don't you?

so are you actually missing the coins or are you talking about the change that gets sent back?

I was just about to post that I see it with "balance" but no "addresses -b".

So if it's mine, how do I find the primary key?

Forgive my ignorance, but why did a transaction of less than 2 BTC need "change" of 107 BTC, and why did that change have to be sent to an address that's not shown in the client?

Ok, everything's fine, but can someone please explain to me the necessity of "change", and the merit of storing it in hidden addresses?

you send the whole balance of the smallest address that is bigger than what you are sending, in your case 109BTC to send 107 back

Because the minimum input you had was of 109 BTC, so it sent 2 BTC to the place where you wanted them sent and it sent 107 BTC back to yourself.

That's the way Bitcoin is designed. Any wallet does that.

Better than any of us, let's just let Satoshi himself explain it to you: http://bitcoin.org/bitcoin.pdf
A simple explanation can be found here: https://en.bitcoin.it/wiki/Change

Why not just send it back to the address that the transaction previously occupied?

Because that would make it obvious to see which was the real transaction and which was the change.

To increase privacy. All transaction stored in blockchain and visible to everyone, by having change sent to another address makes it harder to guess what transaction was the actual payment.

Hm, ok.  I can see the merit of that, although it seems like something that should be optional.  I'd rather keep my bitcoins in a limited number of addresses, so I can easily import them into other wallets.

Thanks everyone.  I guess I've made enough of a fool out of myself for a good while.

Nah, you didn't.

I LOL'ed, can't say I didn't.
But I LOL'ed at your panic, not at your lack of knowledge. ;)

I like to think my panic at losing hundreds of bitcoins was justified, especially since I had no idea where the breach was and whether or not my remaining balance was safe.  My only consolation was that if it was blockchain.info that was hacked, the price of BTC would plummet and I could buy back the ones I lost. :P

Why would bitcoin drop in value if Blockchain.info got hacked? They are just a site among many others.
Bitcoinica got hacked and it had no impact on prices, and if it did it was an increase, as the bitcoin price increased 20%+ since the hack ;)

Hm, good point.  Wasn't it the case last year that a major heist sent the value of bitcoin plummeting?  I guess the market has grown since then.

No, that wasn't the case.
When MtGox got hacked the hacker manipulated the price on the exchange in a way that they went from $XX to a few cents so he could be able to withdraw a lot of them, bypassing MtGox limits, but all those trades were reversed, so, no, the price didn't plummeted in the way you are thinking.
The price plummeting was part of the hack, not a consequence of it on the markets.

I see.  Guess I was misinformed.  So it was just normally market activity that brought the price down to where it is this year?

Yes, it was just normal market activity. As soon as the hack was discovered all trading stopped and was resumed, I think 1 week later, at the price that it was before the hack happened.
Unusual media exposure(Silk Road) was at made the price explode to improper levels in the first place, so it was normal that it went down the way it did.