Interesting reading on NXT forum about peercoin security:
Could someone explain koubiac’s answer below more in details, specifically the second point? Why would nodes work on another blockchain fork rather the one they just accepted? I understand that a fork with 6 blocks will win over one with just one block.
Let's take Peercoin's example to study this possibility.
If the block generated has a timestamp that is larger than current adjusted time + max clock drift (max clock drift =2h in Peercoin) then the block is rejected by the node. ( github.com/ppcoin/ppcoin/blob/master/src/main.cpp#L1889 )
Now let’s suppose the attacker only shifts his timestamp and finds a valid proof only 1 hour in the future. He broadcasts this block which gets accepted by the network. However, in average, the rest of the network will be finding ~6 blocks within one hour so users can continue working on the previous block and the attacker’s block will get orphaned.
Thanx in advance.