Up to now, I use two places to store my altcoin. The first one I use MyEtherWalet for my online wallet. Actually, if we talk about safe and insecure it depends on how we make use of that. All I have to do is be careful in storing security to access MEW, and until now MEW is very safe for me. And sometimes I use Coinomi to save some Altcoin I have. But Coinomi can be used in mobile phones only and used offline. From some of the above answers, you can make a reference to save your Altcoin.