I wanted to make a masternode, truth is that I'm quite new at this kind of stuff. It was ESK coin. I accepted the idea that the coins are probably lost, it was just strange that someone can do this without any other additional information from my part. I have never given away any data, just the public address. This is why it was so strange
It's probably due to security vulnerability on the coin you were working on. I would advise you to have a couple of experts in blockchain field help you set up a masternode and also do some security audits to avoid such attacks. Just because yours got attacked doesn't mean all the blockchain techs and the coins run by them are flawed
Based on your description, I am guessing it was 51% attack. That one attack I know where someone can block transactions by invalidating them and it's easy to carry out on small networks without using many resources unlike Bitcoin. There are ways of avoiding such attacks.