Bittrex account hacked
That's absolutely terrible to here...
More and more I am understanding the need to store the larger amounts OFF exchanges, even if you wouldn't be able to take advantage of that FIRE SALE!!
The blockchain is the public ledger of which addresses have (and had) how much funds. With your 1) crypto address and 2) private key, one can do anything with the funds stored on that address. Hopefully that "one" is "you".
However, with exchanges, it is different. You "do not have" access to that private key. That exchange does. You are much at the mercy of that exchange and their practices. With exchanges, you transact by successfully logging onto their system (username/password). There are now 2 points of failure. 1) your exchange crypto-address/exchange-held private key combination, and 2) your exchange user account
That is why it is "very" important to employ 2-Factor Authentication. The idea behind this is that, even if an attacker has your 1) exchange crypto address/private key, or 2) access to your user account, they wouldn't be able to move your exchange funds without successfully passing that 2nd Factor Authentication, (which for many is the Google Authenticator app on their smartphone, which hopefully only you would have access to at the time of the attempt).
Thank you for letting us know it can happen to anyone. If it is Bitcoin, you are able to track the progress of those bitcoins by searching for your Bittrex exchange bitcoin address in a block explorer.