If you have purchased an authentic copy of the software, then you will have received a serial-number.
My advice: uninstall it, and install the _free_ anti-virus software from Microsoft: http://www.microsoft.com/security_essentials which does _NOT_ require any "key".
Answers & Comments
Orrr if your naughty go to btjunkie.org and get code from der :D
If you have purchased an authentic copy of the software, then you will have received a serial-number.
My advice: uninstall it, and install the _free_ anti-virus software from Microsoft: http://www.microsoft.com/security_essentials
which does _NOT_ require any "key".