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For the people who are reading now, that hasnt 2fa on, I recommend you to do so, as soon as possible.
and if you will lose device or reinstall app which you use for 2fa you will lose and bittrex account )
look at the reviews and feedback about Google Authenticator
u have to write down the bittrex secret key to avoid a situation like u described..............also u should write down the backup codes for the authentificator