I have lots of friends with first hand experience whose account has been hacked with minimum of 3.5BTC lost.
A very close friend of mine personal got email that someone from China logged into his account and carried out bad transactions which he'll never do, like buying bitcoin at high prices & sell his coins at low price. Then got his Bitcoin converted to fiat which he does not have fiat account but the hacker withdrew all his money with a fake registered fait account.
All these fraud & hacking was because these victims failed to activate 2FA. Someone did say that even 2FA (Authenticator) can be cracked once your Google account can be hacked.
This got me wondering if there's internal bot in Bittrex or some sophisticated hacking teams whose specialty is to hack innocent victims.
Final judgment :
Ensure you regularly update your login password with any exchange. Make sure you include Alphanumeric characters with other symbols like #$@&%. Finally, make sure your password does not have anything close to your name, surname or username.
Activate your 2FA for extra protection and ensure no one have access to your email (Google email address).
NEVER you keep more than the exact amount you want to trade with in an exchange. Withdraw whatever profits you have to your wallet account.
If possible, create dual account with the exchange so that you can share the trading money there to avoid having all your eggs in one basket.