Rule 3: Your teenager will destroy your computer

There is no other way of saying it.  If you share your computer with anyone under the age of 21, it will get infected with something at some point.  Usually within 3 minutes of examining a computer it becomes obvious to me that a teenager or teenager-like person has had considerable access to the computer.  As a parent, or adult, if you want to keep your computer clean, the best advice is to not let a teenager use it.  If at all, get them there own computer.  This is even more paramount as we do so much financial and personal business online.  If you cannot do without your computer for a couple of days, keep the kids off of it.  If they use it, it is only a matter of when it will be down for a repair job.  Oh, why does this happen?  Kids do all the things online that you shouldn't do, it really is that simple.  There's a reason you don't let them drive your new car.  Think about it.....