Please be aware that there are phishing sites on the Internet that look like Bittrex. These sites are fake and harvest your credentials which can then be used to login to your account. These sites will capture many different things including, username, password, 2FA code, and possibly even ask you for your email username and password. Bittrex will never ask you for your email username and password, so please never enter those on any login that looks like a Bittrex site.
We highly recommend users enable two-factor to further secure their accounts and protect them from most automated attacks. However, many users will still use the same passwords and email combinations they use on other sites as well as weak password to protect their accounts. Bittrex keeps your user information secure and has never leaked any passwords. However, many sites in the Crypto world have been hacked and the hackers have databases that they attempt to use to login to accounts. This is why we suggest enabling two-factor.