that assumes you do not scan it first for a virus ..... come on man ... we're not amateurs
My guess is that 90+% of the computer aren't computer-savvy enough to do that... you 10%ers can ignore my warning.
Most people buy Norton, install it, and then promptly forget about it, assuming they are protected against viruses for the rest of time, not realizing that new viruses crop up every minute of every hour of every day.
So, while the overwhelming % of computer users have anti-virus software installed, how many of them have the latest virus defs installed? I would guess a MUCH lower %.