I was reading there was a recent 51% attack to Ethereum. Basically, hackers rented enough computer power to get 51% of the mining power, and insert false transactions into the blockchain.
I wonder if such attacks are possible in a Proof of Work type of blockchain, as Tezos. I would assume that requires hackers to own 51% of the coins. According to tzscan, the current market cap of all the tokens is $346,558,758, which is not an insane amount (although, to be fair most of tokens are not engaged in sale orders, as they are standing in baking services; and even if someone wanted to buy a massive amount, this would raise the price and make the transaction much more expensive). Still, compared with PoS type of blockchains, it seems to me that PoW are more vulnerable to 51% attacks. Is this the case? Is there some mechanism by which the blockchain can protect itself from such attacks?