Depends on what you mean.

1) all your data can be entered offline, and it is not shared with TTX Computers  (unless you go thru a special process to create a Diagnostic file to send to TTX agents to check out some computer problem. Pesonal ID information is deleted in this situation.) .

2) connections...when needed..don't go thru a browser, they go directly from your software to the TTX computers thru whatever internet connection you do have.

3) you do have to connect up to the TTX computers to get the software updates....they're still fixing a lot of bugs....and some forms are not finalized.  The early software needs a lot of updates for more complex situations...and late-found bugs.

4)  When e-filing, any additional charges  (usually e-filing the state), do go thru the TTX computer billing system.  The actual file submission goes from your computer, directly to the TTX servers, where they sit and wait for the IRS to pull them off.  Once filed on the TTX server, you cannot get them back...there's no continuing connection.  It doesn't go thru your browser...it goes directly thru your internet connection using whatever security protocols and scrambling TTX has set up for such submissions.

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Added later:

5) if you want to import some tax data from an Online server at a bank, or financial institution...you will have to provide your login information in the software and make an internet connection with whatever tax servers the Bank/Financial institution provides for tax data import..  Otherwise, if you don't trust the software to use it safely, you'll have  to enter that data manually from whatever paper tax forms those providers give you.