they were hacked years ago, it's still not truly safe to keep your earnings on their exchange, you should send them away to your own wallets and exchanges, but they're very user friendly and no-fuss, the small scale payouts and withdrawals make it much better for alot of people mining on only 1-3 gpus, you can move your earnings around quicker and easier than most exchanges.
Start your mining career here, then move on elsewhere if it suits you.