What's the minimum amount of internet security software I need?

The Single Most Important Internet Security Tool

The most important tool you should run is not something you may think of as an internet security tool at all. And as important as it is many people don't run it, and they should.

In my opinion the single most important tool you can run when you're concerned about internet security is a regularly scheduled backup.

No, it won't protect you from anything - however what a good backup will do is allow you to recover from almost anything that happens to your personal computer.

And don't fool yourself into thinking that with the right protection you'll never have a problem - it can still happen even with the best available security setup possible. There's simply no such thing as perfect security. Even if you're doing everything right your machine runs a risk of still getting infected. Having a backup - ideally an image backup of your entire machine - will allow you to "undo" whatever problem might arrive on your machine with absolute certainty that the issue is gone.

That's something that only a backup - or a reformat and reinstall - can do.

The Big Four

The basics of computer security software fall into four basic buckets: firewalls, anti-virus tools, anti-spyware tools and staying up-to-date.

Firewall

You need a firewall. This can be in the form of a router that you computer connects to the internet through, or it can be software installed on your machine.

I prefer the router approach, because it requires no additional software on your machine. Routers are inexpensive, and they give you complete protection against network based threats coming in from the internet.

Alternately you can make sure the Windows Firewall is enabled, or you can install additional more comprehensive firewall software that would monitor outgoing as well as incoming network behaviour.

Firewall: you need one. And you only need one.

Anti-virus

You need a good anti-virus package. There are many, of course, and there are a few free ones I recommend.

Anti-virus is one of the areas where I see people thinking "if one is good, two must be better!". Unfortunately it doesn't work that way. As you've pointed out many anti-virus solutions install software that runs continuously to monitor for incoming threats. Unfortunately, if two (or more) different anti-virus tools both have this continuously running software they can come into conflict with each other. The result at best is a slower system, and at worst is viruses being missed, or benign files being erroneously flagged as containing a virus.

Anti-virus: you need one, and should only have one installed and running at any given time. It's sometimes handy to have additional packages available to help diagnose a threat as needed, but only as needed. They should never be installed and operating continuously. For most folks I recommend settling on a single anti-virus tool and leaving it at that.

Anti-Spyware

You need a good anti-spyware package. This is in addition to your anti-virus tool. While the line is often blurred between the two, viruses and spyware are technically two different animals, and the corresponding anti-virus and anti-spyware tools use different techniques to do their jobs.

Once again, there are many, and once again there are a few free ones I recommend.

Anti-spyware: you need one, and once again like anti-virus you should only have one running at a time. Anti-spyware tools also have components that run continuously and if multiple anti-spyware tools are running at the same time they can come into conflict.

Staying Up To Date

Vulnerabilities are being discovered in software all the time. They may be the result of bugs that have been in place for years, or they may be the result of unplanned for usage scenarios, or they may simply be an unexpected side effect of a recent bug fix or feature addition. Regardless of the reasons, vulnerabilities are being discovered regularly in all software, and as a result new malware is constantly being written to immediately take advantage of those machines that have yet to be patched to resolve the problem.

The solution is simple: stay up to date.

In general, that means making sure that Windows Update is enabled and configured to automatically install updates. Make sure that your anti-malware tools above, as well as most applications on your machine are also configured to update automatically as well.

Automatic Updates: turn them on.

Beyond the Basics

The tools above are enough. In fact, they represent what I actually run on every machine I own. Beyond these basics I rarely see a need to install or run additional tools, scanners, protection services or whatnot on a PC. I know some feel otherwise about some favorite tool or service that they're quite happy with; that's great. You can evaluate each on it's own merits, but my position is that they're not required, particularly when looking for the bare minimum tools to run.

Common Sense is Not Optional

Contrary to what I said above, the most important security tool isn't actually software that you install on your computer. It's not a service you sign up for, and it's not a website you visit.

The most important security tool is really you.

There is no security setup that will protect you from yourself. If you elect to visit questionable web sites, ignore warnings that you don't understand, allow software to be downloaded and installed on your machine regardless of its source, or regularly click on links or open attachments in email you don't recognize ... nothing you install on your computer will protect you.

The good news is that common sense requires no RAM, no hard disk space and takes no CPU cycles.

You just have remember to use it.