Confirming Payment ... 1 block, 2 blocks, 6 blocks?

[Stephen Gornick]

I sent a 1 BTC payment to MyBitcoin.  At about 10 minutes later I got the Payment Notification email acknowledging the transfer.  But my own client still showed unconfirmed.

When I logged into MyBitcoin ..., my Balance showed the 1.0 BTC.

Is the number of blocks needed before "confirming" a transaction something that is subjective?  I.e., why does the Bitcoin client wait until a different number .. (6 confirmations, I think ... ) to change to Confirmed, than what MyBitcoin uses?

[theymos]

MyBitcoin probably considers a transaction confirmed after 1 block. The more confirmations, the more difficult it is for the sender to reverse a transaction. 6 is almost impossible (and never profitable), but 1 is still extremely difficult. Even 0 is quite difficult. The last few pages of the Bitcoin paper have probability calculations for this.

Maybe MyBitcoin requires more confirmations when you deposit larger amounts of BTC.

[Stephen Gornick]

A nice thread on Confirmations from today as well:
  http://bitcointalk.org/index.php?topic=1994.0