An anti-virus software should be reliable and not slow down your computer. It should do 
its job and not even be noticed it is running. Norton Anti-virus, especially its Internet Security suite, has been very overbearing, sluggish, and sometimes ineffective. McAfee is a decent, slimming anti-virus software, but make sure you register online or else you might not get ongoing updates.
Kapersky is an easy installation, and uninstall if necessary, and provides an easy interface. Some software make it very difficult to figure out how to kick off a manual virus scan or where to find past malicious threats. Not Kapersky – there is a minimalist, almost Google-like, interface to make everything easy to find. It was the fastest among its competitors in scanning and installing virus definitions. Another factor that is very important, but often overlooked, is that Kapersky is not well-known, like Norton, making it stealth-like for those viruses intended to infect more popular security software.