This is still a work in process.
Keep all of your software up to date.
I use Secunia Personal Software Inspector (PSI). This is free for home, non-commercial use.
Another tool you can use is filehippo .
Modify your system to do security updates frequently.
Get a hardware-based firewall.
Get a hardware based firewall between you and the Internet. Your cable modem doesn’ count. The “Firewall” on your computer does not count. Make sure you change the default password.
1. Install a hardware-based firewall If you have a high-speed connection (i.e. not using a telephone dialup line) you should get a dedicated firewall router. If your vendor has provided you with one
OpenDNS
Advanced tools
http://blogs.technet.com/b/yuridiogenes/archive/2011/05/25/identifying-unexpected-activity-using-sysinternals-tools.aspx
Install TCPView
Install Process Monitor
http://technet.microsoft.com/en-us/sysinternals/bb896645
Microsoft has a new security scanner that augments their virus detection software
http://www.microsoft.com/security/scanner/en-us/default.aspx
A good write-up on this is here
http://andrewtechhelp.com/tech-news/windowsoffice-news/120-microsoft-safety-scanner
Microsoft has a package that will remove rootkits
They have a bootable disk image you can use to remove spyware
http://connect.microsoft.com/systemsweeper
Mailware Removal Guide
http://www.selectrealsecurity.com/malware-removal-guide
Firefox Plugins
NSA Has some suggestions
http://www.nsa.gov/ia/_files/factsheets/Best_Practices_Datasheets.pdf
The FCC has Ten Cybersecurity tips for small businesses