Quote from: BubbleBoy on July 06, 2011, 02:50:46 PM

It's pretty clear that rewriting the history is not equivalent with stealing everybody's money, rather it means destroying the system and making the coins worthless, so the likely attackers will not be profit-motivated by any definition of profit expressed in bitcoins.

There would be an incentive, by double-spending coins and making a profit that way, see example above.

Quote from: BubbleBoy on July 06, 2011, 02:50:46 PM

The hashing power of the network already surpasses what could be accomplished by ~10 million commodity PCs, excluding even the largest botnets as worthy attackers.

About 99.8% of the hashing power of the network is currently paid for by temporal rewards of 50 bitcoins per block.