It is possible that having multiple anti-virus programs installed on the same computer can cause problems between each. For this reason it is not suggested to install more than one of the programs with "*"s, or installing either program when another anti-virus (McAfee, Norton, ect.) are installed.
Microsoft Security Essentials is a anti-virus program offered by windows that you can download and use for free on computers with Windows installed. On windows 8 and on all of the operating systems after this comes installed already and is called Windows Defender.