you can protect as many computers as you need from a single account. As long as your buying the correct amount of license's. According to thier website, it says that only Norton Internet Security 2007 or Norton 360 can be used on 3 machines with the purchase of one license. However, if you go to the local Best Buy or Circuit City, you can find Norton Anti-Virus with protection for 3 machines, and thats for one license.