Bitcoin Forum

Hello friends i am much worried ...
2 days ago one exchanger send me btc but still not confirmed.Few minutes ago my transaction had reversed back to exchanger account.
what is a double spending attack or not?
and how payment reversed.and now a time double spending attack is possible?

It is not an attack, it is a feature.

If the transaction is not confirmed it's the same as it didn't happened.

Unconfirmed transactions aren't secure (https://bitcoin.org/en/you-need-to-know#instant)

Say goodbye to that money.  Gone.  Sorry about the bad luck.

This is how double spend works.  They set up a transaction (first spend), then when it falls as unsuccessful, they spend the same money on a different address/transaction (second spend). 

The first transaction 'didn't happen' like the guy said above.  Therefore, you are out of your money and fucked. 

Bitcoin is very complex.  Most people just get robbed and then quit.  Please be careful.  Anyone can just log in to your computer and get all your savings in an instant. 

True, it's quite complicated, up until now the only thing I know is how to send and receive money on my online wallet. Still confused with the technical stuff. Does this mean he wouldn't get his money back? That would suck  >:(  Do you think this is possible to avoid? I'm currently learning stuff like Photoshop and later I'll take some CAD seminar. Planning to freelance IRL and probably also advertise my service OL in this forum. This incident made me uneasy. What if I already sent them the finished project and then the payment I received ended up like OP's transaction? If the client is like half-way accross the globe, obviously I wouldn't be able to sue to them (or at least show up outside their office to pester them to give me my payment) :(


I'm curious OP, what did the exchanger sent you coins for? Is it like profit from money you deposited or you're taking back money you deposited? Well, you don't have to answer it, I'm curious how you got into this arrangement.

I don't think that exists attack that is called double spending, this could be kind of feature, error or scam attempt. You haven't mentioned which exchanger is in question, there are also some suspicious ones. The worst thing here is that you have actualy lost your coins and that you will not get them back.

Contact that exchanger with all proofs you have about that withdrawal and if they are legit than they may send you again. I think that transaction dropped from the mempool after not getting confirmation for many hours or even days because transaction may not have enough fee which is currently around 100 satoshi per byte of transaction size.

Contact them, actually what is the name of that exchanger you have used.

Sometimes the transaction isn't picked up in a block if the sender didn't include a sufficient fee.  If it isn't picked up in a block and they "accidentally spend" the intput with an appropriate fee in a separate transaction then your transaction will be voided.  It could be a mistake....contact the sender.

you mean it could be back to the sender?. I consider it a big problem if it didn't get back to the sender. And it can happen to anyone if this is determined by the sender. The recipient cant always be responsible for transaction fee.

By exchanger you mean someone who traded with you not bitcoin exchange? You should notice that earlier before finishing the deal.
Never send anything first, always wait for at least 2 confirmations. Or  you can use escrow service when dealing with random people from the internet.
Pity that you didn't include more details like transaction ID or the name of that individual who scammed you.

You must be very smart and very fast to get your bitcoin into your second wallet before the original sender double spends your money.  If you don't understand where your keys to your second wallet (protected) are, you won't do this right and you'll lose all your money.  You can't just leave your bitcoin floating out there where the other guy can spend it again. 

Please be careful.  You can lose everything in an instant.  One mistake, and your money is gone forever. 

Yes...If the transaction stays in the mempool for too long and all the nodes carrying the transaction drop it, then the transaction would be cancelled and the bitcoin would still be available in the senders wallet.  The sender is responsible for including the transaction fee, not the receiver.

EDIT This could be the problem: https://bitcointalk.org/index.php?topic=1801057.msg17942880#msg17942880

seems you got your money back
seems you are just curious why it came back and wondering should it have came back

short answer if the transaction is not confirmed after a while it just drops off the network as if it nver happened.
it appears coinbase noticed this(in green) and gave you the balance. so you are back to where you were, no loss no gain.

the main reason a tx doesnt get confirmed is that the tx fee isnt high enough. there is no fee that is a 'guarantee' and at the moment the devs are arrogantly avoiding a proper working 'priority' formulae/code to sort the issue. all they are saying is "pay more" like bitcoins limited blockspace should be treated like an auction house whre you have to declare a higher bid then others for a chance.

That is why it is always a rule to wait for one confirmation before you send your goods/services/alternative money/etc. If you did it through a website though, you should file a scam accusation for this.

I have read something about that on blockchain.info that if your transaction isn't confirmed it will just come back to them.

So maybe your exchanger does have the same thing with blockchain.info once your transaction isn't confirmed, they will just come back to them.

Have you tried to check it out again?