Why is the 2017 TT showing up in Finder as TurboTax Deluxe 2018? It also created a 1-byte app of TurboTax Deluxe 2016. Is there a worm or virus in the download?

It looks like you already had an application with name "TurboTax Deluxe 2017" in your /Applications directory. 

During installation Mac default installer would ask you to "Replace" existing app or "Keep Both" or "Stop" installation process (refer attachment). If you choose "Keep Both" then OS would rename "TurboTax Deluxe 2017" to "TurboTax Deluxe 2018" before placing application in your /Applications directory.

Reasons for "TurboTax Deluxe 2017" application already present in /Application directory i.e.

1. Either, you installed "TurboTax Deluxe 2016" version twice in past and choose "Keep Both" option accidentally during 2nd install. So, it would place 2nd copy of "TurboTax Deluxe 2016" application in your /Applications directory after renaming it as "TurboTax Deluxe 2017".
2. Or, you already installed "TurboTax Deluxe 2017" application and repeating above steps.

Kindly move existing copy of "TurboTax Deluxe 2017"  & "TurboTax Deluxe 2018" applications inside /Applications directory to Trash and try fresh install again.

Please confirm if it addresses your problem.