Anti virus software helps in protecting your computer(s) from viruses. However, simply installing anti virus protection is not enough. There are spyware and adware threats that your anti virus software might not be able to tackle. To keep your computer clean of all malware, you also need antispyware in addition to anti virus protection. Though most anti virus packages carry antispyware protection, I recommend you to have a separate antispyware such as the free Windows Defender (which comes pre-installed with Vista and Windows 7; you need to download Windows Defender from the Microsoft website for Windows XP). Plenty of other free antispyware programs exist for non MS operating systems such as: Anti Virus Guard (AVG).
In addition to the anti virus software and antispyware, you also need a good firewall. Some of the anti virus software comes with built-in firewalls but most of them are just anti virus protection. For Vista and Windows 7, you can use the default Windows firewall as it is strong enough. For previous versions of Windows, I suggest using ZoneAlarm or Comodo Firewall. You can check out the top ten Firewall comparison based on my experiences with different firewall software.
You can also include other security software that tells you if you are visiting a clean website, phishing filters, anti spam software, etc. Plenty of reviews exist on Brighthub that help you decide what all computer security software to use, based on how you use your computer. I also use Winpatrol to make sure that none of the external programs change my computer/Internet settings.
To sum things up, you need a minimum of three components to stay safe while computing, especially if you spend most of your time on the Internet. They are: Anti Virus Software, Anti Spyware Software, and a Firewall. You can include additional security software if you wish.
Note: For best anti virus protection, use only a single anti virus package. Using more than one anti virus software will create conflicts that may ruin your computer security. If you install an external firewall, remember to turn off Windows Firewall from Control Panel.
Now that we know the basic components of computer security, let us check out some of the best antivirus software on the market.