From the Wiki:
If the attacker has the majority of computer power, "the attacker can't reverse other people's transactions without their cooperation."
I don't quite understand why this must be the case. Let's say attacker wants to undo a transaction
k that happens at block
i. Why can't an attacker with a majority of hashing power start mining a block
j originating with block
i-1 that includes everything but
k? Then, the attacker will succeed in the long run and the transaction
k no longer appears in the longest chain, right? So I'm not quite sure why you cannot reverse other people's transactions in a majority attack.
Diagram for clarity:
-i(includes k) -i-1 -j(does not include k)...(this chain should be longer w/ majority computing power)