Today, honestly, the most important shield against malware of any kind is not anti-virus, but anti-spam/tracking. And most people don't use any. Using ABP plugin for your browser, and a good anti-spam program such as Adaware or Spybot S&D is more important than whatever anti-virus software you choose. Getting a virus that actually works is rare. Quite rare. People get tracking/spamware every single day that anti-virus software does nothing to prevent.