Yes POS helps is a better method for securing the netwok because it is more resistant to 51% attack. In a POW minting , if one node has 51% or more of the network's hashing power, it can possibily perform a 51% attack.
But to perform a 51% attack in POS system you'll need to have 51% of the total coins in circulation, which is highly impossible. In this case one needs to have more than 50billion coins to do a 51% atttack.

Actually its both.
actually POS is also a way of minting. but it doesn't take any of the cpu or other hardware's power.
POS is a method of mining blocks called stake-blocks. In this case after 20 days a transaction is recieved, that transaction becomes eligible for POS minting. So instead of using the hashing power of your hardwares the POS minting uses the no.of coins and coin-age of that transaction to mint the Stake Block. The reward also depends upon the no.of coins and coin age, meaning  when a transaction mints a Stake block it calulates the stake percentage for the transaction for the un-rewarded coin-age. In this case you'll recieve an average of 25% p.a during the first year