[odrekf]

So how does Coinbase do it?

[lojack]

Coinbase uses cold storage. They have some reserves in hot storage, but presumably less funds accessable makes them a smaller target. Correct me if I'm wrong, but I believe they are able to pull this off because they aren't technically an exchange. Coinbase Exchange may be all in hot storage, but they provide a seamless way to transmit your exchange reserves to a cold storage backed wallet.

[teod]

Couldn't find too much information on this, but I see that [https://support.gdax.com/customer/portal/articles/2436336] under "Is GDAX's ether hot wallet insured?" states "The majority of ether and bitcoin deposited to GDAX is held in highly secure cold storage." (GDAX is Coinbase's exchange platform) See also [https://www.coinbase.com/security].