Keep it up to date, run a regular scan, and let it check your incoming messag¬es. Without this, your PC is virtually guaranteed to be infected.
Update antispyware
This may be bundled with your AV; keep it up to date and scan occasion¬ally. It's a good idea to install a couple of antispyware apps, such as Windows Defender (it comes with Vista) and Spy Sweeper.

Use a bidirectional firewall
Prevent unwanted inbound and outbound traffic on your Pc. Two-way firewalls come standard with Mac as and Windows Vista. Users of older Windows versions should get a thirdparty firewall such as CheckPoint's ZoneAlarm.
Don't mix multiple firewalls or antivirus software , It might seem like twice the protection to have two firewalls, but it's likely to double the headaches. Same with dual A V. (Antispyware is another story.) Allow auto updates Let Windows and Mac as update when they want to, since Microsoft and Apple are constantly patching any security holes they find.

Don't accept EXEs
Downloading executable files (ending in .exe, .com, .bat, and .scr) is hard to avoid, but be wary of those e-mailed to you. That goes for .doc and .xls files as well; they can carry macro-based viruses.

Route traffic
If you have broadband service but don't have a router, get one. Wired or wireless, they're cheap. Activate the hardware firewall Your router should support NAT (network address translation) so Internet users scanning for open ports to exploit can't see your computers, It should also support SPI (state-ful packet inspection) to distinguish legitimate network traffic from bad. Don't turn these features off.