Quote from: Boba on July 30, 2014, 08:41:22 AM

It's my understanding that in order to successfully double spend you need to be able to mine your own block. And shorter block times makes that alot easier to do. So 10 min block time makes it very hard to double spend in bitcoin.

This is just one kind of double-spending attack...called the Finney attack after Hal Finney. It's the hardest to defend against but also the most costly to perpetrate. Most double-spends would be simply sending one transaction to the target and another to the rest of the network and hope that the target has not protection against that.

Fast block times increase orphans and increase the amount of hashing that is wasted since miners will be mining on the wrong block more of the time. 10 minutes was a good guess. At least it wasn't 30 minutes or an hour. Litecoin's 2.5 minutes appears to be working out ok but time will tell as transaction volumes go up which is better.