<p>The <a href="https://en.bitcoin.it/wiki/Double-spending" rel="nofollow noreferrer">wiki explains it better than I can</a>:</p>

<p>But the short answer is that's the reason most participants <a href="https://en.bitcoin.it/wiki/Confirmation" rel="nofollow noreferrer">wait for at least 6 confirmations</a> before accepting a transaction as valid.  The likelihood of hash collisions or other potential attacks having any success going undetected drops with each confirmation, and 6 confirmations is usually chosen as an "overkill" number.</p>

<p>To answer your question from the post title, though, refer to this question's answers:</p>

<p><a href="https://bitcoin.stackexchange.com/questions/722/has-there-ever-been-a-successful-double-spend-attack-on-the-bitcoin-network-if?rq=1">Has there ever been a successful double spend attack on the Bitcoin network? If not, is it really necessary to wait for confirmations?</a></p>

<p>If what they say is correct, it seems we really don't know if and when (or how often) any double-spends have actually been successful.</p>

CC BY-SA 3.0
2013-08-22T19:05:04.407Z
2013-08-22T20:42:51.623Z
2017-04-13T12:47:36.647Z
Neil Neyman
<p>Judging from this list, not very often:</p>

<p><a href="https://blockchain.info/double-spends" rel="nofollow">https://blockchain.info/double-spends</a></p>

<p>Why is this the case? I would have guessed they would have been more frequent.</p>

<p>Is it OK to always accept (small-to-medium) transactions as valid then?</p>

<doublespend>
How often do double spends happen successfully?
John Devor
# How often do double spends happen successfully?

(Asked by: username_0 on 2013-08-22)

Judging from this list, not very often:

<https://blockchain.info/double-spends>

Why is this the case? I would have guessed they would have been more frequent.

Is it OK to always accept (small-to-medium) transactions as valid then?

**Tags:** doublespend


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## 1 answers

### Answer by username_1 on 2013-08-22. Score: 1

The [wiki explains it better than I can](https://en.bitcoin.it/wiki/Double-spending):

But the short answer is that's the reason most participants [wait for at least 6 confirmations](https://en.bitcoin.it/wiki/Confirmation) before accepting a transaction as valid. The likelihood of hash collisions or other potential attacks having any success going undetected drops with each confirmation, and 6 confirmations is usually chosen as an "overkill" number.

To answer your question from the post title, though, refer to this question's answers:

[Has there ever been a successful double spend attack on the Bitcoin network? If not, is it really necessary to wait for confirmations?](https://bitcoin.stackexchange.com/questions/722/has-there-ever-been-a-successful-double-spend-attack-on-the-bitcoin-network-if?rq=1)

If what they say is correct, it seems we really don't know if and when (or how often) any double-spends have actually been successful.


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