antivirus software project

Hi, I want to know if you can create a software antivirus only to eliminate de most frecuent virus. (The reason is because I gonna to create a web page ) and? I gonna to offer the software to the public. I want to know how often can be the antivirus update.? Especifications: 1.- the software, must have the antivirus data-base most common.? 2.- the software have a easy download. 3.-? we accept advice and sugestions to do a better bussines.? and the software runs on winXP.? ?