I keep my bitcoins and altcoins in trading website like yobit, cryptopia, livecoin, etc. because this websites are user friendly.
Are you sure that you are keeping your bitcoins at yobit.net? There are a lot people that are complaining about that trading site. So if I were you, think again because in the end you will have problem on it when you are experiencing withdrawal problems.
I've also heard the same bad sounds against Yobit.net even if you follow the threads on the altcoins section you'll find many complaints against this exchange site like poor support, user also experience of withdrawal problem and more. It's not good suggest to keep our Bitcoin such of this third party site, more better keep it cold storage.
There's a lot of them, just visit the scam accusations board and you'll see a lot of people are complaining about their balance on yobit but most of them are from alt coin wallets but still you should be cautious with that trading site, it's very unsafe to keep your bitcoins there. But still that's your bitcoin, you may store them whatever you want to prefer.