For these reasons, it’s understandable that Bitcoin traders and owners will want to take any possible security measures to protect their holdings. To do so, they utilize keys and wallets.
Bitcoin ownership essentially boils down to two numbers, a public key and a private key. A rough analogy is a username (public key) and a password (private key). A hash of the public key called an address is the one displayed on the blockchain. Using the hash provides an extra layer of security.
To receive bitcoins, it’s enough for the sender to know your address. The public key is derived from the private key, which you need to send bitcoins to another address. The system makes it easy to receive money but requires verification of identity to send it.
To access bitcoins, you use a wallet, which is a set of keys. These can take different forms, from third-party web applications offering insurance and debit cards, to QR codes printed on pieces of paper. The most important distinction is between “hot” wallets, which are connected to the internet and therefore vulnerable to hacking, and “cold” wallets, which are not connected to the internet.
In the Mt. Gox case above, it is believed that most of the BTC stolen were taken from a hot wallet. Still, many users entrust their private keys to cryptocurrency exchanges, which is essentially a bet that those exchanges will have stronger defenses against the possibility of theft than one’s own computer would.