I have enabled 2 factor authentication in both of my accounts in bittrex and poloniex to remain in safe side. And I also suggest you to do so, it doesn't require iphone or any high priced smart phone. You can use any android smartphone that can run google authenticator app.
It is pretty simple, try it.
thank you mobnepal , i already enabled 2 factor authentication ;
but 2fa Is it enough ? If sufficient,
Why all the exchange ( yobit / bleutrade/poloniex) sites have added the feature ( Email Code. To enter your account )?