Not sure how one can know for sure.
If you suspect that, log into your account and change your password. (write it down, you will forget).
______________________
That being said...NEVER EVER click on a link in any email that seems to come from TurboTax. There is at least one pfishing email that looks exactly like a TurboTax email, but if the user clicks on the link in the email to log in,,,,,the sleazeball criminals steal your login information (and maybe your SSN too)
____________*Answers are correct to the best of my knowledge when posted, but should not be considered to be legal or official tax advice.*