Why a bitcoin confirmation is needed??

[bitc0in]

Bitcoin once sent are sent,so why a bitcoin transaction over network is waited by some merchants,people or atms.It's just that until confirmation the bitcoins aren't considered usable.But to make transactions and dealings faster why wait for confirmations then??

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[DannyHamilton]

Bitcoin once sent are sent,so why a bitcoin transaction over network is waited by some merchants,people or atms.

Until the transaction is sufficiently confirmed, there is a small risk that the transaction could be cancelled in some special circumstances.  Some people either don't understand the risks or are overly cautious.

It's just that until confirmation the bitcoins aren't considered usable.But to make transactions and dealings faster why wait for confirmations then??

Some merchants don't wait for confirmations.  It all depends on the risk tolerance of the merchant and their understanding of the risks they are exposed to.

[BitCoinDream]

Bitcoin once sent are sent,so why a bitcoin transaction over network is waited by some merchants,people or atms.It's just that until confirmation the bitcoins aren't considered usable.But to make transactions and dealings faster why wait for confirmations then??

According to the claim of bitundo.com, they can reverse your Tx, if it is not confirmed.

[bitc0in]

Bitcoin once sent are sent,so why a bitcoin transaction over network is waited by some merchants,people or atms.It's just that until confirmation the bitcoins aren't considered usable.But to make transactions and dealings faster why wait for confirmations then??

According to the claim of bitundo.com, they can reverse your Tx, if it is not confirmed.

Is there any instances of reverse in transaction or any such.??

[bitc0in]

Bitcoin once sent are sent,so why a bitcoin transaction over network is waited by some merchants,people or atms.

Until the transaction is sufficiently confirmed, there is a small risk that the transaction could be cancelled in some special circumstances.  Some people either don't understand the risks or are overly cautious.

It's just that until confirmation the bitcoins aren't considered usable.But to make transactions and dealings faster why wait for confirmations then??

Some merchants don't wait for confirmations.  It all depends on the risk tolerance of the merchant and their understanding of the risks they are exposed to.

Yeah many do accept while not confirmed as well,but for the ease why don't everyone just not wait for confirmation and make btc payments more viable

[DannyHamilton]

Yeah many do accept while not confirmed as well,but for the ease why don't everyone just not wait for confirmation and make btc payments more viable

Everyone?

You can't force someone to accept something that they don't want to accept.

[DannyHamilton]

Is there any instances of reverse in transaction or any such.??

Yes.  With under the right cirsumstances transactions have been replaced.

[BitCoinDream]

Bitcoin once sent are sent,so why a bitcoin transaction over network is waited by some merchants,people or atms.It's just that until confirmation the bitcoins aren't considered usable.But to make transactions and dealings faster why wait for confirmations then??

According to the claim of bitundo.com, they can reverse your Tx, if it is not confirmed.

Is there any instances of reverse in transaction or any such.??

Here is a thread of a successful double-spend => https://bitcointalk.org/index.php?topic=152348.0

Keep an eye on this page => https://blockchain.info/double-spends

U might catch one.

[InwardContour]

You have to wait for some confirmations before spending bitcoins because there is a little possibility that the coins you have received were double spent.

[homm88]

All users are still urged to seriously consider all bitcoin withdrawal addresses, and cause them to still valid and beneath your control. It's strongly recommended to incorporate aliases to bitcoin addresses, and delete any obsolete or incorrect addresses promptly.

[Brewins]

There are several double spend attacks that not confirmed transactions are vulnerable. Or at least more vulnerable.

See the details:

https://en.bitcoin.it/wiki/Double-spending

The decentralized anti-double spend depends on confirmations. They would not exist without a purspose

[Loophole]

The more confirmation the transaction has, the more difficult (exponentially) a double-spend can be done.

For me, if the transaction amount is small, the transaction has standard fee attached, the transaction has no dust outputs or unconfirmed inputs, and no double-spending attempt is noticed after a while (eg. a minute), I don't have problem accepting the payment.

[Loophole]

All users are still urged to seriously consider all bitcoin withdrawal addresses, and cause them to still valid and beneath your control. It's strongly recommended to incorporate aliases to bitcoin addresses, and delete any obsolete or incorrect addresses promptly.

I can no point deleting addresses from your wallets for a few reasons.
1. Deleting a few private keys won't save you much storage space.
2. You never know when you will need to use those "obsolete" addresses (eg. recovering your bitcointalk account, your old friend sends you some bitcoin to your old address)
3. If you suspect some of your private keys are leaked, you should create a new wallet on a clean machine, and send all your bitcoin to your new wallet ASAP. But still, you should keep a copy of the old wallet just in case you may need it some time in the future.

[themys]

its for security matters else you are not sure you receive the money, the ultimate security its to wait 6 confirmations.

[bitsmichel]

Bitcoin once sent are sent,so why a bitcoin transaction over network is waited by some merchants,people or atms.It's just that until confirmation the bitcoins aren't considered usable.But to make transactions and dealings faster why wait for confirmations then??

Confirmations are needed to prevent abuse of the system. Without confirmations, how can you be certain a transaction did occur?

[hilgi]

Are there any percentages of bad transactions if we don't wait for confirmations? I am working on a platform which takes small payments, 25 cents or so, as of now we are not waiting for confirmation to start our system. Any idea about how many we can expect to be bad?

[elise]

not sure exactly, but its whenever a miner finds your bitcoin.

[AllTheBitz]

Keep people from scamming the network.

[Sonny]

its for security matters else you are not sure you receive the money, the ultimate security its to wait 6 confirmations.

There is no "ultimate security" and the number 6 has nothing special to it. The more confirmations the transaction has, the more difficult it will be double spent.
It all comes down to your risk tolerance.
For example, some casinos and exchanges are okay with 1 confirmation, some ask for 2 or 3, while some ask for 6.

[CoinCidental]

all depends on transaction value really

for a cup of coffee or a do-nut i  would take the risk .....

for a new smartphone  or a laptop  id tell them to sit down and relax until i see some confirmations