This game isn't a laiden with DRM like most of the current PC offerings. Your subscription fee and account is your DRM. So you could technically have the game on a hundred machines. Just one person per account at a time.
Heck, you could go to a friend's house who also has the game and play your account by simply using your login credentials.
This is because the characters are stored server side. This actually has a double effect:
1: you can log into the game from anywhere
2: you can rest assured that no one is editing their character saves to get extra stats.