Cryptocurrencies are stored in online wallets, which can be done through exchanges (e.g. Coinbase offers Bitcoin wallets) or through wallets that you can install on your own computer. Major exchanges have been hacked, but most of them take steps to ensure that customers’ funds are secure. Many major exchanges store the majority of their assets offline (on computers that aren’t connected to the internet). As for personal wallets, as long as you take steps to keep your information secure, your cryptos should be safe. But don’t forget or lose your wallet codes.
Sven Franssen