What happens to double spend transaction?

[goxed]

Is the first transaction picked up and the second dropped? or are both dropped? or are the btc lost for ever? Thanks!

[1714905809]

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[sedeki]

Afaik, only the first transaction is accepted.
The rest of the bitcoin network will not accept the second transaction.

[Stephen Gornick]

Is the first transaction picked up and the second dropped? or are both dropped? or are the btc lost for ever? Thanks!

The context is important here.

Most mining occurs using the Bitcoin-Qt/bitcoind client which will reject any double spend attempts.   So it is the first transaction to reach the miner is the one that gets included in a block.

So how a "race attack" double spend works is if the attacker knows your IP address and you take incoming connections, the attacker has one node shoot a spend transaction to you.  Then at the very same time the attacker has another node shoot another spend transaction to the rest of the network.  The attacker's aim is to have you see the transaction (0/unconfirmed), then you hand over the cash or whatever reason the coins were sent, and then only later when the mined block arrives would you realize that the funds were double spent.   There are protections against that (don't allow incoming transactions, for outgoing you have an explicit connection to well-connected nodes.  Additionally, even if you do accept incoming, you can check the rest of the network (e.g.,blockchain.info being one source) before handing over any value to see if any double spend transactions were broadcast.

That's the typical race attack.  There's also the Finney attack, the 51% attack, and others.
 - http://en.bitcoin.it/wiki/Double-spending

What is the context in which you are asking?

[goxed]

Okay someone stole BTC from me today. No idea how. I am quite surprised that it happened. My wallet was unencrypted and was created in 2011.
The thief's transaction did not have any fees so was not picked up when I came to know about the theft.

Thereafter I copied an old wallet.dat and replaced it and created a new transaction with a fee. I want to stop the thief from getting my btc.

http://blockchain.info/double-spends

[goxed]

Theft http://blockchain.info/tx/ad30186ab82a59770ba6dbe891846f4dc2c31c61b0f8e72229180ecf146ef18f

[DannyHamilton]

Theft http://blockchain.info/tx/ad30186ab82a59770ba6dbe891846f4dc2c31c61b0f8e72229180ecf146ef18f

Me http://blockchain.info/tx/9955c0f61291f47ff32d245fa9da1316287fbaf9e6c596468037058e4b7a69dd

The thief's transaction already has confirmations.  That means it has already been included in a block.  Your transaction will never confirm.

The only way your transaction could confirm would be if there is a reorg and the theif's block is orphaned, but since the thief's transaction already has more than 11 confirmations, this is almost certain not to happen.

[goxed]

I guess its a lost cause now. Armory installed.

[doobadoo]

Thereafter I copied an old wallet.dat and replaced it and created a new transaction with a fee. I want to stop the thief from getting my btc.

http://blockchain.info/double-spends

Do not re-use the old wallet for receiving new coins.  If all your coins are gone, delete the wallet.dat and create a new one.  Just creating a new address with the old wallet will still leave you vulnerable to a re-theft.  The compromised wallet file must go.

Also, what OS are you using?  Is it windows?  Don't bitcoin and windows.  Run linux, or os x and only install software from the appstore/package manger.

[doobadoo]

did you ever upload this wallet to an online backup service or email it to your gmail or something similar? 

Also, why the fruit are you not using a password?  its the only thing that prevents theft if you wallet.dat is lifted from your hd.

[goxed]

I donot exactly remember maybe I had emailed it to myself using yahoo mail.  . This is a wallet from early 2011, and it was created as a hot wallet on a windows computer. I was amazed that some thief could get a copy of it from somewhere. It's a Windows 7 computer. I am now using armory. Are you aware of tools to check for hidden keystroke loggers? I guess the best secure solution is an offline wallet.

[doobadoo]

I donot exactly remember maybe I had emailed it to myself using yahoo mail.  . This is a wallet from early 2011, and it was created as a hot wallet on a windows computer. I was amazed that some thief could get a copy of it from somewhere. It's a Windows 7 computer. I am now using armory. Are you aware of tools to check for hidden keystroke loggers? I guess the best secure solution is an offline wallet.

STOP USING WINDOWS.   Also don't email an unencrypted wallet.  In theory a devious yahoo employee could search for attachments containing wallet.dat

Go download some linux.  Install it to a big flash card or usb drive/stick.    Or learn how to partition your hard drive and dual boot.  Only install bitcoin on the version of linux.   Don't mail your wallet to youreself unless its encrypted.  you will keep coins secure.

[goxed]

I donot exactly remember maybe I had emailed it to myself using yahoo mail.  . This is a wallet from early 2011, and it was created as a hot wallet on a windows computer. I was amazed that some thief could get a copy of it from somewhere. It's a Windows 7 computer. I am now using armory. Are you aware of tools to check for hidden keystroke loggers? I guess the best secure solution is an offline wallet.

STOP USING WINDOWS.   Also don't email an unencrypted wallet.  In theory a devious yahoo employee could search for attachments containing wallet.dat

Go download some linux.  Install it to a big flash card or usb drive/stick.    Or learn how to partition your hard drive and dual boot.  Only install bitcoin on the version of linux.   Don't mail your wallet to youreself unless its encrypted.  you will keep coins secure.

Thanks for the suggestions.
All my miners are Linux. in 2011 bitcoind and bitcoin-qt did not have encryption features. I have now created a new wallet and immediately encrypted it. I am concerned that there could be a keystroke logger on the windows pc. You are right I should keep all wallets in *nix pc.