Quote from: ranochigo on November 28, 2015, 08:24:06 AM

Quote from: Amph on November 28, 2015, 07:49:14 AM

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Quote from: javierfjavier on November 26, 2015, 11:19:33 PM

Well, first of all hi to everybody, i'm a newbie in this cryptocurrency thing, so a lot of doubts are in my mind these days.
I have this question, looking here for the answer I didn't found yet, basically the subject says it all.

If bitcoin transactions are irreversible, why some platforms (online wallets, exchanges, etc) need X confirmations to "validate" a transaction?

You answered yourself. Exactly due to fact that bitcoin transaction are irreversible it is wise to wait for at least 1 confirmation of the network.
Unless there is 1 (or more confirmations) there is a risk of 'double spending' of bitcoin.

Even with 0 confirmations the risks of double spend are insanely overblown. Unless you are paying a lot for something really important, then chances are you can be perfectly ok with 0 confirmations and sleep better at night, certainly better than credit card transactions.

The risk is not zero though. Double spends can happen so why not prevent them?

With waiting for a few confirmations you stop double spending, and assure you receive the BTC. So I think it's worth it and we will people continue to wait.

they actually happened a couple of time, and i remember one of them was with okpay https://bitcointalk.org/index.php?topic=152348.0

It happened only once in Bitcoin's history. Of course it could have happened again if the merchant didn't run a full node in the recent chain fork. In the incident you said, the merchant wasn't on the correct fork which no amount of confirmations would help. There isn't much protection against this except to cease payments if a fork is reported or network alert is issued.

it's actually two times and maybe three i have my source, the second one is this https://bitcointalk.org/index.php?topic=327767.0

p.s. third one is a perhaps, it was told to me by an user in one post, i don't remember it anymore, but maybe i'm confusing it with the second one, but anyway you have two attempts