First the basic, "big three":

Anti-virus programs scan for viruses and related malware by examining the files on your system for patterns of data that have been identified as being viruses. On some regular basis the database of patterns the programs use is updated to contain the latest information on known viruses.

"In short, you should have one each of all three."

Anti-spyware programs monitor your system as you use it for behaviours that are known to be spyware-related. For example, an anti-spyware program might trap attempts to change your browser home page, or attempts to install software that starts automatically.

Firewalls prevent malware from reaching your machine through your network. They don't prevent things you control, like downloads or email, but rather stop attempts to connect to or infiltrate your machine without your knowledge or participation.

In short, you should have one each of all three.

It's seems simple, but sadly it's not.

"Internet security suites" are, in essence, bundles of two or more of the basics above, and typically also include additional security software or shortcuts as well. For example, one extremely popular internet security suite contains all three: anti-virus, anti-spyware and a firewall, as well as calling out "phishing" protection, keylogger protection, website reputation information, email and download monitoring, spam filtering, parental controls and even throws in some PC performance tools to boot.

Everything but the kitchen sink, it seems.

Once again, on the surface it seems like a good idea. Who wouldn't want all that?

Based on my experience here at Ask Leo! I've become fairly biased against internet security suites or bundles. I see several problems:

I get more problem reports about security suites than I do with the individual programs that they replace.

From what I can tell, most suites are based on one very good program - say an anti-virus tool - and then add additional tools and features, typically of lower quality, simply so that they can claim a longer checkbox list of features.

Much of what these suites call out as separate features are, in fact, fundamental to one of the big three tools anyway. Saying you have "keylogger" protection and spyware protection, for example, is redundant.

Much of what these suites include is also unnecessary, or not something I'd go to them for. I wouldn't use my internet security suite to try and tune up my PC, for example.

But, that's what internet security suites are: they give you a lot of stuff in a single package; some of it good, some of it not so good, some of it, in my opinion, completely unnecessary. And with so much stuff being added to your system, it's not at all uncommon for the suites to in fact cause both functional problems and system performance issues.

Now, there's one other point of confusion that's worth addressing: the growing convergence of spyware and viruses and the technologies that scan for them.

You've probably seen an increase in the use of the term "malware". That's a generic term meaning "bad" "software", and is used to encompass viruses, spyware and in fact anything else that might come along.

The problem is that the line between viruses and spyware isn't nearly as clear as I've painted above. And as a result, the scanning and prevention technologies are also overlapping more and more. In fact, some tools are now starting to label themselves as simply anti-malware, since their approach and their coverage seems to straddle the definition.

Unfortunately, it leaves us in an interesting position: if you know you need both anti-virus and anti-spyware tools, is a single anti-malware tool sufficient?

Maybe.

It all depends on the specific tools involved.

My recommendation for determining which tools are right for you, and which might be better than others, is simply to do some research on the internet. I'm a huge believer in reputation as a guideline. While no tool has a perfect reputation, you'll often see both good and bad information that will allow you to compare relative merits.

But, ultimately ... well, I told you it was a confusing mess.