I suggest that you used a secured site when storing your bitcoin online. You can if its a secured site by just seeing the green lock next to the url of the following site you are using. First of all if you want to securely buy and hold onto bitcoin use a exchanger that is easy used and have many verification and confirmation before you can withdraw your bitcoins. My advice also to you that you must used two wallets , the one is for storing your bitcoin and the other is for trading your bitcoin.