When you run the free check, this website keeps the domain you checked in your browser's session storage for the rest of your visit. A button you choose next can then carry it to the portal, to start a plan or get the Full Report, or into the contact form. It is never sent anywhere unless you follow a link that carries it. Your browser clears it when you close the tab.
The portal sets the cookies it needs to keep you signed in.
If your IT provider gives you OuterMark, the portal also sets one that remembers which provider, so its sign-in pages wear that provider's brand. It holds nothing about you, and lasts a year.