I'd like to give a simplified overview of how your defensive systems work.
The average home computer has approximately 64,000 ports through which it can communicate. By default these ports are open and can be used by any programme which cares to access them, either from within the computer or from without. If you were to go online with a computer in this condition you would quickly be attacked and your computer would be infected.
To prevent this you install a Firewall. A firewall will close all open ports and you then open the ones you need by setting "rules" for them according to the instructions supplied with the Firewall programme. Usually you will have ports open for your Internet Browser, your e-mail client, and the update functions for various programmes.
These "open" ports will not be fully accessible, in that they will only allow a communication if it was instigated from within your computer. Any unsolicited communications from outside are blocked.
However if you are tricked into starting the communication, then as far as your Firewall is concerned it is a legit transaction and it will open the port. So by clicking on malicious links, replying to unsolicited e-mails and attachments, and downloading from unsafe sources, you are effectively bypassing any protection your Firewall supplies.
At this point your Anti-Spyware and Anti-Virus programmes take over. The real-time-protection in these constantly scan the data stream in your open ports looking for things that match with items in the database they have within them. If they find something then they will alert you, or quarantine it, or delete it, according to the rules set within the programme.
However as you can see, if the database does not contain details of the infection that's attacking you, then your Anti-Virus or Anti-Spyware programmes will not protect you. There are new infections (or new variations of old infections) created every day, which is why it's vital to keep your programmes up to date. Even with a fully updated database though, you are still playing catchup, which is why your Firewall, Anti-Virus and Anti-Spyware programmes cannot ever give you 100% protection.
Adding more and more programmes will not
give you more and more protection, it's up to you to take some responsibility for your online actions, and modify them to give your programmes the best chance of protecting you.Be careful what you click on.
- Don't download anything from a site you do not know and trust. Remember, there's no such thing as a free lunch, if something seems too good to be true it is. Malware purveyors love to offer out freebies as bait knowing full well that one unguarded click is all it takes.
- Don't reply to unsolicited e-mails.
- Don't open e-mail attachments (even from friends) without checking with the source to ensure they actually sent them.
- Don't use P2P file sharing programmes. Even the ones that don't come bundled (and many do) are not safe. By using them you are effectively downloading from an unknown source, with all the dangers described above.
The bottom line is, you can never remove all risk, but you can minimise it by being careful online.