I have heard from some Vista users that Windows Defender can be a bit confusing when it comes to Microsoft SpyNet. In a typical Vista scenario, you can open the Start menu, type in 'def' in the Start Search, and open up Windows Defender. This is a useful tool that basically keeps an eye on pertinent system changes. If there are unexpected changes, chances are good that you will be notified. Defender can stop spyware and other technical diseases on your system. It cross references your system and software changes with those of other Internet users to come up with a general consensus of what is safe or not.
The confusion I refer to above is with Microsoft SpyNet. In Windows Defender Home, you can see below the Microsoft SpyNet this description: "Join the online community that helps identify and stop spyware infections". I am sure Microsoft intends no confusion by this and its use of "membership" terminology, but some people interpret this to mean possibly a subscription is needed: in other words, sign up and pay up . But in fact this is not a fee based service, it rather provides for some optional means of using Defender: there is basic versus advanced membership or no membership whatsoever, and there is no sign up. If basic or advanced is chosen, software classifications information is sent to Microsoft, but it is very little, and in fact advanced is recommended.
Basic and Advanced SpyNet memberships are similar, with one key exception: in Basic membership, you will note the following line: "With basic membership, Windows Defender does not alert you if it detects software or changes made by software that has not yet been analyzed for risks." Yet, that is exactly the protection that is needed and only 'advanced' membership can provide.
For that reason, it is advised that you choose advanced membership. And indeed there is no fee involved!