Here they are :
1) Check Windows Update and Office Update regularly by visiting Microsoft Update site or by clicking on the Automatic Updates Tab in the system Control Panel and choosing the appropriate options.
2) Installing a Personal Firewall.
3) Installing a free Spyware Blocker.
4) Block Pop Up spam messages by disabling the Windows Messenger service by opening Control Panel >> Administrative Tools >> Services >> Right Click Messenger >> Properties >> Set Start-up Type to Disabled and press the Stop button.
5) Using Strong Passwords and Changing them periodically.
6) If you're using outlook or outlook express, use the current version or one with the outlook security update installed.
7) Buy Antivirus Software and keep it up to date. If you're not willing to pay then try Free Editions.
You may also give a try to these Antivirus Softwares listed below i.e.
8) If you have a Wireless Network, Turn on the Security Features like using MAC filtering, Turning OFF SSID Broadcast and even use WEP with the biggest key you can get.
9) Join a respectable E-mail Security list.
10) Be Skeptical of things on the Internet. Don't assume that E-mail From a particular person is actually from that person until you have further reason to believe it's that person. Don't assume that an attachment is what it says it is. Don't give out your password to anyone even if that person claims to be from support.
So these are Top 10 Tricks to enhance free Security.