The recent 51% attack news really interests me, so my friend and I take some time to look into it. And what we have found is shocking. The current cryptocurrency world is extremely vulnerable. See for yourself.
http://www.cryptoattack.io/risk
We compare the cost of taking over 51% hashing power and the liquidity of the specific crypto and then compute the return ratio of attack. we get Data through nicehash and whattomine, update every 10 minutes.
From the result, especially the coins forked from Bitcoin or Litecoin, they are most likely to suffer from this attack if given enough liquidity.