I suggest you to download and install Microsoft Security Essentials from the following address
http://windows.microsoft.com/en-us/windows/products/security-essentials
If you have questions about it, go to the related Answers Forum at the following address
http://answers.microsoft.com/en-us/protect
You could also try posting question related to Defender Offline Beta in this Forum.
Bye.
Luigi Bruno - Microsoft Community Contributor 2011 Award