Bitcoin Forum

https://blockchain.info/address/1AcAj9p6zJn4xLXdvmdiuPCtY7YkBPTAJo

Is this true, and if so, how was that possible?

It means that this address has received Tx which was double spend. But, AFAIK, if u receive Tx, which is part of an orphan block, ur address will have this warning, till ur Tx does not get fit into another block in the longest chain.

https://www.ghash.io/

43.81 Ph/s
TRUSTED BY 180K USERS

https://blockchain.info/address/1CjPR7Z5ZSyWk6WtXvSFgkptmpoi4UM9BC

I perfectly know that, you don't look very clever by posting it.

If you have no answer, or anything of use, it's not mandatory to post.

I would like to know why that happens.

Mhhh pardon my noobness, you mean that it was a transaction that was sent and confirmed in one block and then in another block for some reason?

someone is using enough hashing power to duplicate the transactions, u should be able to trust transactions from the address as long as you wait for 6 confirmations

in normal bank note terms a double spend is when you hand someone a $10 note, they mistakenly hand it back as change and you can spend it again..

in bitcoin terms it SHOULD BE:
where a bitcoin is sent to 2 destinations (transactions) and both get confirmed..

this true double spend NEVER has happened and cant under current bitcoin conditions.

but anyone can send out the same transaction twice. but only one will get confirmed, and the other transaction wont get a confirmed bitcoin to use.
now the problem is that some places accept unconfirmed transactions and release products, goods or services even before its confirmed, which from a human observation of handing out funds and receiving goods is considered a successful double spending. but observing the blockchain is not a successful double spend.

basically do not hand out goods, services or products before the received coin is confirmed, and you dont have to worry about double spends

https://blockchain.info/double-spends

in short:
you wont find a single output being used twice where both destinations get confirmed, its purely about the merchants noobness to hand out funds/goods before confirmed

OK this is good info and good explanation, thank you, but then how do you explain the warning given in this data when the source is a trusted one?

You mean this warning: "Warning! this bitcoin address contains transactions which may be double spends."

Shouldn't it say attempts of double spending? As I understand it, double spendings cannot survive on the Bitcoin block chain for long. Unless the whole Bitcoin protocol has been compromised!

its a warning. to merchants that do accept non confirms to never trust funds from the source address that sent that transaction..

think of it like a shop that has a photo of someone that handed them a counterfeit bank note that last time they didnt check if it was real straight away. thy are just warning people to be aware of the guy sending out double payments, and to ensure they confirm the payment before handing out goods to that person


in my eyes it should be worded 'attempts' but as the quote in my last post say's:
"Double spends on this page may be unintentional. In the event that a double spend is maliciously crafted being listed on this page is no indication that it was successful or any merchant or user lost money as a result."

meaning that their mindset is that although its not a blockchain double spend, it doesnt mean that its not a merchant double spend (not waiting for the confirm).

so its always best to wait for the confirm to be sure its a real bitcoin you hold in your receiving wallet.

Oh, scary! When buying with bitcoins in a shop for example, then it's too long time to have to wait 10 minutes for the transaction to be completed. Doesn't this mean that people could use hacked wallets that double spend all the time?

False Bitcoins ? Holly... i wonder if this is just a bug, passing issue or a huge stinky trouble that may cause Bitcoin to crash  :'(

No, it's ordinary bitcoins that are spent. It's just that attempts can be made to spend say 1 bitcoin two times, double spending. The double spending will be refused to be successfully added to the Bitcoin block chain. However it takes about 10 minutes for a Bitcoin transaction to be completed, and during that time the shop owner will not know if the payment will be made.

websites such as overstock. take days to deliver goods. so its easy for them to wait for confirmations. but as for the "starbuck's" scenario of waiting 10minutes + for payment before they even pour the coffee into a cup. that is simple to get around

PRE-PAY (research: officially called offchain transactions)

imagine starbucks had their own online wallet service you register and deposit lets say a weeks worth bitcoins for coffee and cookies. and thats confirmed on the blockchain. and starbucks 'credits your account with that X btc

now when you physically walk into starbucks you pay using the starbucks wallet and pay through the wallet. the starbucks wallet is nothing more then a sql database balance to show how much people have pre-paid.

that way starbucks know they are getting paid, because technically they have already been paid. the customer is just agreeing to drop his balance by X amount on the stabuck sql database (offchain).

On the second page, you can see a transaction that was not confirmed.
https://blockchain.info/tx/ced06cedbfbc0895cdaec6f7065d8c9248797acd1da47796a8885ddd1e0c4a96

If you follow the block, it shows it as orphaned
https://blockchain.info/block-index/448192

So that's it, it's an address that found a hash for a block that ended up being dropped. That coinbase transaction didn't get confirmed and
the address was flagged as suspicious. Nothing wrong though.

Regards,
--h

Thank you everybody for your help clarifying what's going on.

Still, there's something unexplained.
How can a merchant even ISSUE two times a spending of the same bitcoins?
How can this happen in an "automated" way, because I suppose I can't double spend my bitcoins from my bitcoin wallet, right? So it must be something coded somewhere, right?
And if this is coded, how to trust the issuer of those bitcoins again?




I agree that Bitcoin times are too long for everyday shopping.
But I think this will be replaced by some web wallet service, there are already many and it's easier to rent some service like this than to build own infrastructure, I think.

Do you mean in general or in this particular case?
In general, if someone intentionally sends a double spend they shouldn't be trusted anymore. That's the reason for this warning.
In the case you mentioned, it is not a double spend. The miner found a solution to a block and was rewarded for it. But because someone else found out a solution to the same block and his chain ended up being longer, the former miner had his reward rescinded. This is why rewards take 100 blocks before being confirmed.

There are several ways this can occur.  Some are malicious, some are accidental, and some are out of the control of the user entirely.


It can happen intentionally from custom written wallet software, it can happen accidentally from users of the blockchain.info wallet that send a transaction without a fee.


That depends on the wallet you use.  Some wallets (such as blockchain.info) make it so easy to do that people often do it accidentally.  Other wallets such as Bitcoin Core make it much more difficult to do.


Not necessarily, but possibly.


Wait for confirmations.