If you have installed Microsoft Security Essentials you might have seen that you are automatically enrolled in the “SpyNet” program with a “Basic membership”
Microsoft SpyNet is the network of Windows Defender and Microsoft Security Essentials users that help determine which programs are classified as spyware. The signatures created for any submitted programs by the users of the product are available to all users, displayed as a bar graph that shows the percentage of people who have allowed, blocked, or removed an item. This method of spyware classification allows rare, unknown, or new spyware to be categorized as most people choose to send their data.
Luckily since version 2.0 users can now completely opt out from within Microsoft Security Essentials by going to Settings tab selecting Microsoft SpyNet and then selecting the I do not want to join SpyNet radio button:
Additionally if one would like peace of mind the following entries can be added to the %windir%\system32\drivers\etc\HOSTS file in notepad:
127.0.0.1 Spynet2.microsoft.com 127.0.0.1 Spynettest.microsoft.com