Verify imported blockchains from peer nodes

[cosme12]

Loaded node_peers blockchains should be validated. find_new_chains() should verify the new imported blockchain follows the requirements. This prevent attacks that attempt to completely change the blockchain history.

[jrmtoubRHL]

If i understand correctly, In order to verify the hashes , we need to do the POW done by the miner again? In bitcoin , when nodes verify transactions , they have to do the same costly POW as the miner? Thank you