As we all know, a Antivirus system is a must on your computer today but unfortunately this is not always the case if you look at your friends and family computers (and even if they have one it is not updated). So here is two very good tools (and free) that will help you get some free dinners if you invite to help you friends and family
Microsoft Security Essentials
A real-time protection that helps guard your home or small business PCs against viruses, spyware, and other malicious software
Note that Microsoft Security Essentials is also available for small businesses with up to 10 PCs
Microsoft Standalone System Sweeper
Microsoft Standalone System Sweeper Beta is a recovery tool that can help you start an infected PC and perform an offline scan to and identify and remove rootkits and other advanced malware. In addition, Microsoft Standalone System Sweeper can be used if you cannot install or start an antivirus solution on your PC.
Note that Microsoft Standalone System Sweeper is not a replacement for a full antivirus solution providing ongoing protection; it is meant to be used in situations where you cannot start your PC due to a virus or other malware infection.