There are many ways to provide security, one of which is to keep harmful elements away from those parts or people they may want to damage. Exclusion is often the only way society can defend itself.
Many companies are offering to protect our PCs for free
It is much the same for people that go online, where the main focus of security is keeping our data safe.
The big players like Symantec, McAfee and Sophos offer huge suites of programs aimed at protecting you and your computer online.
But there is an alternative. A growing number of programs from smaller firms are aimed at the security market are available to download free of charge.
More often than not these programs are meant to entice you to upgrade to the full version, which costs money.
Zone Labs do just that with a free version of their firewall product, ZoneAlarm. But offering software gratis does more for the company than just expand its potential customer base.
"We get a lot of experience from the free version, so by having 35 millions copies of ZoneAlarm out there we're able to understand what is the threat environment, and provide a more secure proposition to our paid user base," said Laura Yecies of Zone Labs.
But as you would imagine, some people - for example the manufacturers of products that you pay for - do not think it is such a good idea to trust the family data to a free security product.
"We've seen plenty of examples where an attacker will actually create their attack either in or as part of a free security tool," said Greg Day of McAfee.
"We've seen examples where maybe you think you've got a bit of spyware [on your computer], something trying to steal a bit of information or some kind of attack, and you go to the internet and to try and find more and perhaps get a free tool to get rid of it.
STAYING SAFE ONLINE
Use anti-spyware and anti-virus programs
On at least a weekly basis update anti-virus and spyware products
Install a firewall and make sure it is switched on
Make sure updates to your operating system are installed
Take time to educate yourself and family about the risks
Monitor your computer and stay alert to threats
"Now maybe the good ones will actually get rid of that attack but at the same time they may drop maybe 10 or 20 other attacks onto your system."
The bottom line, according to Mr Day, is that when you download free security software you cannot be certain what you get.
But completely free security software may be a thing of the past when the new version of Windows hits the shops early next year.
Windows Vista, as the new operating system is known, brings a whole new way of dealing with how data is controlled within the operating system.
Essentially, programs, including Microsoft's own, will not be given the privilege to write data just anywhere on the computer as they do in XP.
"[The new] Internet Explorer is not able to write to the main areas of the file system, it can't overwrite Windows," said Microsoft's Stephen Lamb.
"So if I visit a website I don't have to worry that a keylogger or a root kit, or some of these things that you hear about in the press, are going to get onto the system."
Laura Yecies of Zone Labs said: "Microsoft is certainly making it more difficult for the independent security vendors right now.
"They're essentially trying to take control of the security user interface functions.
"Fortunately we have a pretty crack team which is finding new and innovative ways to continue to provide a very important security layer to our users."
So the antivirus people are having to hack Windows so they can get close enough to protect it. Microsoft does not see it that way, though.
"The question I would ask is 'do I want third parties, other than the manufacturers of the kernel (the core code of a computer's operating system) that I'm using, making changes to that?' Because making changes, even to access controls, can have a direct impact on the reliability and integrity of the system," said Mr Lamb.
"That's really why Windows Vista's been re-architected - to protect itself from external access."
At the same time as Microsoft starts closing off parts of the operating system to security software vendors, it has also released its own security product known as OneCare. The all in one package is designed to look after your computer and all your data, leaving the whole gamut of security on Microsoft's shoulders.
Let us hope they are broad enough.