Quote from: anderl on June 17, 2013, 03:02:30 PM

might be some FUD in the OP's threats

You can't just magically create coins out of thin air and you can't change the block chain history.

https://en.bitcoin.it/wiki/Weaknesses#Attacker_has_a_lot_of_computing_power

An attacker that controls more than 50% of the network's computing power can, for the time that he is in control, exclude and modify the ordering of transactions. This allows him to:

Reverse transactions that he sends while he's in control
Prevent some or all transactions from gaining any confirmations
Prevent some or all other generators from getting any generations
The attacker can't:

Reverse other people's transactions
Prevent transactions from being sent at all (they'll show as 0/unconfirmed)
Change the number of coins generated per block
Create coins out of thin air
Send coins that never belonged to him
It's much more difficult to change historical blocks, and it becomes exponentially more difficult the further back you go. As above, changing historical blocks only allows you to exclude and change the ordering of transactions. It's impossible to change blocks created before the last checkpoint.

Since this attack doesn't permit all that much power over the network, it is expected that no one will attempt it. A profit-seeking person will always gain more by just following the rules, and even someone trying to destroy the system will probably find other attacks more attractive. However, if this attack is successfully executed, it will be difficult or impossible to "untangle" the mess created any changes the attacker makes might become permanent.

It's easy to double your money on each attack. Send to an exchange, reverse transaction, withdraw. Or, send to exchange, trade for bitcoin, reverse the transaction.

Edit: By the way, that last paragraph in your post is only true for currencies with significant hash rates.