Cryptocurrency exchanges are convenient but unsafe. Blockchain, the technology underlying cryptocurrencies, was designed to fend off cyber attacks. However, this only works if users stay true to its principles.
All cryptocurrency addresses are tied to a private and public keys. The public key allows users to send money to that address, while the private key allows its owner of the key to send money to other addresses. With that your funds are secure if you keep your key private.
Exchanges store private keys on behalf of their users. And in return the exchange enables their users to easily trade between cryptocurrencies and fiat.
Having all private keys in one place encourages cyber attacks on exchanges and therefore creates a less secure and private environment for the end user. Although, many exchanges have an extensive security teams, attacks on exchanges are sill being made.
Cryptocurrencies, in their core, aim to create a safe and secure trading environment. Exchanges can create a flaw in that environment. Therefore we suggest that you hold your funds in a private wallet, and only send funds to an exchange to trade.