Lots of misinformation here. NXT is not a clone of Bitcoin, it was written from scratch using java + javascript and has almost nothing in common with Bitcoin aside from the general concept of using a blockchain.
How is this blockchain secured, if not by mining? (honest question)
Please, if you never heard about Proof-of-Work and Proof-of-Stake, use google.
It is quite long to explain.
Phrased my question wrong, sorry.