Pinpointing The Threat

This is actually pretty simple. To find out how someone can break into your system, you must understand why they do it. Generally you can narrow it down to plain and simple greed.

People just don't take over your system if they have nothing to gain. That's one fact that has never changed since the dawn of man. So I'll give you a rundown on why there are people who would love to take over your PC via the Internet, and how they do it.

Hijacking

Ahh.. The age old art of hijacking your PC. In less techie terms, it generally means an attacker who gains full control of your PC to make it do something that he wants (and generally what you don't want). It could be anything from using your PC to attack another PC or a server, sending out spam, modifying the contents of your own PC, etc. Your PC is practically at his command once he hijacks it.

However, hijackers don't do it for fun. They generally hijack your PC for three things - attacks, propagation and referrals. When used for attacks, the hijacker usually uses your PC to attack a webserver as part of a larger DDOS (Distributed Denial of Service) attack. In propagation, the hijacked PC is used to send out spam or hijack other PCs by using an infection vector. Finally, referrals, being the most annoying of all, generally means an attacker hijacks your PC to relay you to websites that earn them money through referrals.

Spying

Is there an easier way to get money than through stealing a person's login to his/her online banking site? If you're good enough at it to obtain tons of logins by infecting thousands of PCs, you can even get away with it by just stealing 10 bucks from their owners. Most will not even realize they have just lost 10 bucks, and even if it's a relatively small amount of money, replicating the theft hundreds of times gets you tens of thousands of dollars.

There are, of course, other reasons why people would love to spy on you. It may not mean much, but the details and statistics of your surfing habits are very valuable commodities. Even the tracking of the webpages you visit can be profitable information for those who are in traffic modeling. And where there's profit, there's bound to be somebody lurking in the shadows waiting to make a buck or two at your expense.

Generally Annoying The Heck Out Of You

Some people just like to demean your PC and make it do stupid things before dying. Maybe it's just to stroke their dumb egos or something. Yes yes, even that's a legitimate reason.

Seriously, there are a lot of viruses, trojans and attackers out there that just latch on to your PC and create havoc for the perverse enjoyment of their creators. So, let's put a dent in their joy, shall we?