Kraken is a US-based cryptocurrency exchange that operates in Canada, the EU, Japan and the US. The exchange claims to be the “the world’s largest Bitcoin exchange in Euro volume and liquidity.” in January 2018, Kraken went down for 48 hours while it performed an upgrade which was intended to only last for two hours, the longest the exchange has been suspended trading. Kraken charges a fee for every trade that you execute on your account. the total fee is dependent on the total cost (value) of your order, that current pair that is being traded, your 30-day volume (in USD), and whether your order is maker or taker. Additionally, Kraken charges extra fees if you are trading on margin.
Kraken can laud over the fact that, since its inception in 2011, it has never been hacked. The exchange also offer some of the most rigorous procedures in cold storage wallets that are well “air-gapped.” Their system security is also state of the art featuring armed guards and separate internal networks.