Logging into your online account won't affect anything else like QuickBooks etc. You only have to log into the same online account to install and activate the program. Then to file a return you can use your own account and they use their own accounts. And the returns are only on the computer that filed it. They are not in the online account so no one else can see your return, unless they use your computer.
If you don't want to give them your account info to install it then you enter your account on the computer to install and Activate it. They won't see your account username or password and won't see any of your personal info or returns, etc.
