go to this link to see the differences http://shop.symantecstore.com/store/symnahho/en_US/ContentTheme/ThemeID.106300/pbPage.NISNAV09_flashCompare/pgm.12018200
Give you a free anti-virus.I saw mentioned that it is cloud based.I tested,you can have a try.Quite nice speed and use less memory.Nice software and even its freeware.