Yes, you can.
Signing into your FileFactory Premium account on multiple computers which you own, or while you are away travelling is fine.
However, publicly sharing your login details will result in your account becoming automatically suspended.
Also you will find that you can only be signed into one FileFactory account at a time. For example if you are signed in at home, then sign in at work, you will probably receive an "IP address mismatch" error. You'll then be signed out of both accounts, and will need to sign in again. Once you've signed in, there should be no more problems.