Why 6 confirmations?

[dominicus]

Why do many bitcoin services implement 6 confirmations before BTC credit?
What's so special about 6 vs. 5 or 2?

[bitcoin44me]

Which one?

I think that most services are requiring 1 or 3 confirmations.
It is to prevent double spending. The higher the number of confirmations is, the lower the risk is.


But it will delay the transaction.
Most of the time, 1 confirmation is enough.

[dominicus]

mtgox, and if I recall correctly, coinbase & bitpay post BTC transfers after 6.

I understand the part about lowering double-spend risk, but why not implement a risk-based wait period?  If the transaction is for smaller amounts, wait for fewer confirmations and viceversa.

Seems like a lost opportunity to speed up the network.  May be a trade-off between pursuit of a consistent user experience vs. mitigating overall fraud risk.

I was just wondering if there were any technical aspects behind this, 6 confirmations being ~1hr, might have been related to the ability of the network to spot a forks in the blockchain or such.