To purchase directly from Intuit/TurboTax online, the only valid website is https://turbotax.intuit.com/personal-taxes/past-years-products/
Make ****SURE**** you select the link for the specific tax year you need. After you pay for it, you can then download the installation file. After download, double-click the installation file to install it on your windows computer.
NOTE: Make sure you pay for the correct version, be it MAC or WINDOWS. If you buy the wrong one, you own it.
