Types

• Some antivirus software runs all the time on your computer, watching what happens and looking for signs of virus activity. Other types, such as online scanners, run only when prompted and look through all of your system files and personal documents for signs of infection. When used regularly, both types of antivirus software can prevent and remove virus infections.
  
  (see Reference 1 & 3)
  
  

Function

• Antivirus software works by looking for the binary signature of known viruses. If one is found, the user will be prompted for what action to take, such as removing the infected files, restoring the system to a known good backup or taking no action at all. Many antivirus packages also look for suspicious system behavior that could be an indicator that a previously unknown virus is present.
  
  (see Reference 3)
  
  

Features

• In addition to detecting and removing viruses, many antivirus software packages provide additional features. These may include the ability to monitor incoming email attachments for viruses, monitoring network ports for unauthorized access attempts or monitoring your instant-messaging program for people trying to send you a virus.
  
  

Cost

• Because viruses and other forms of malicious software are a global threat, many companies offer basic virus detection and removal software for free. Modern versions of Microsoft Windows come pre-loaded with Windows Defender to help shield against viruses and spyware. For more advanced features, such as faster scanning and more frequent updating, some companies offer premium packages at varying costs.