Network security is a type of constructive lie that we tell ourselves, as a method of making ourselves feel more secure about where we are in spite of all of the evidence to the contrary. The sad fact of the matter is, no matter how much we may work to be secure in the online world, there is always going to be a serious threat to our computers out there. And as troublesome as it is to admit this, we are never going to know what that threat is until it has hit at least one or two of us (and it will usually have hit more by the time we catch on to its existence and methods).
For every information technology worker doggedly following up on every suspicious action on a network, there is at least one hacker looking for a way to get past every screen which currently exists. The simple fact of the matter is, every screen which exists right now is only there as a response to an attack which happened at some point in the past. Getting ahead of hackers is about as impossible as stopping germs which have not yet been developed- neither have the antibodies. While the hackers of the world sit at their terminals puzzling out ways to get past the defenses, technicians on the defensive can do little more than wait and wonder what is coming up next.
This is why you need to be careful what websites you go to, and where you put your information. While firewalls, scanning programs which identify known viruses and online encryption are a good series of steps to take toward making your online experience a more secure one, you are never going to be absolutely secure so long as your computer can connect to the millions of others which could be out to take it over and steal information.