Couldn't find too much information on this, but I see that [https://support.gdax.com/customer/portal/articles/2436336 https://support.gdax.com/customer/portal/a

Couldn't find too much information on this, but I see that [https://support.gdax.com/customer/portal/articles/2436336 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 https://www.coinbase.com/security].