Norton Antivirus is definitely the most used Norton Activation used now. The software is pre-installed on more or 80% of all new Windows based computers which is good thing because most consumers buying new computers are likely to have either Dsl connection or a Broadband. Each computer connected to the Internet requires Anti Spyware or an Antivirus installed while online. What most consumers don't know is this software is installed as a trial subscription. If you blow off the renewal warnings which mean your protection software won't be upgraded? Most virus protection software make use of a database of understand viruses that compare the files in your hard disk.