Most new computers come with antivirus software already installed, but it is usually just a trial version. If you like the look and feel of the antivirus software that comes bundled with your computer, you might want to consider upgrading to the full paid service. It will probably save you the most time, and you can rest assured knowing it is a trusted product since it was installed by the manufacturer.

The following are some the most common features of the most popular antivirus programs. Determine which features are most important to you and make sure that the antivirus software that you purchase offers those features.

On-Access Scanner
Scans files as they are manually opened or accessed by other applications to ensure that they are free of malware.

Real-Time Scanner
Monitors network data as it is transmitted to your computer to intercept any malware that may try to permeate your system.

On-Demand Scanner
Provides the user with the ability to manually scan files, folders, programs or entire drives for any malicious code at will.

Compressed File Scanner
Compressed files such as ZIP or RAR archives used to be convenient ways for viruses to slip by undetected. With the compressed file scanner, even compressed files can be scanned to determine if they contain any malicious programs or infected files. More advanced antivirus software will do deep scans that can detect harmful files that are deeply compressed and hidden under several layers.

Heuristic Scanner
Uses advanced technology to evaluate files and determine if they are a potential threat even if they contain no known malware by comparing them with patterns observed in most types of malware.

Scheduled Scans
Provides users with the ability to schedule scans in advance, so that they can be performed when the computer is not being used.

POP3 Email Scans
Monitors incoming and/or outgoing email traffic any associated file attachments to determine if there are any threats.

Script Blocking
Monitors Java, Visual Basic, ActiveX and other similar script files to detect malicious activity (script languages are the primary means of executing malicious code from web sites).

Webmail Protection
More advanced antivirus programs provide users with the ability to monitor web-based email from providers such as Yahoo! Mail or Hotmail to scan file attachments for malware. More and more email providers are beginning to provide this service to their users, so this feature may not necessarily be a deal breaker.

Instant Messaging Protection
Instant messaging traffic is scanned for potential threats, if any are found they are then blocked. Worms and other malware are commonly spread via instant messaging programs.

Automatic Virus Database Updates
The most important aspect of any antivirus program is that it is up to date. As stated earlier, new malware is unleashed every single day. The best antivirus software providers constantly update their databases of known threats and send automatic updates to their users to provide maximum protection. This option can be turned off if you prefer to manually accept updates.

Automatic Software Updates
Many antivirus programs will routinely send out updates that improve their ability to detect new threats. Similar to virus database updates, these automatic updates can be switched to manual.

Regardless of which antivirus software you choose, the most important factor is that it is a trusted brand with frequent and thorough updates. It is strongly recommended that you enable automatic updates to ensure you get the most benefit from your antivirus product.