Sharing - Open to anybody?!?

When I invite somebody to one of my spreadsheet, it includes a direct link to see the file...

So... "Anybody" (with that link" can see my data?!?! They do not need to be logged in????

Is there something I don't understand here?

I don't want anybody to be able to see the data unless they are logged in (to verify their identity). No?

Can somebody explain to me how to do that?

Thanks in advance.
darcyk