Is “Defender” enough, or do I need additional anti-malware tools?

In this excerpt from
Answercast #74, I look at some confusion around "Defender" and versions of
Microsoft Security Essentials.

Multiple anti-virus programs

So this is a case where I believe Microsoft has done us a grave disservice
in the way they've named things.

The "Defender" that comes with Windows 7 is, in fact, only an anti-spyware
product. It is an anti-spyware scanner. So yes, absolutely - you do need
something else in addition to that.

That's not true for Windows 8. For people who are reading or listening to
this and thinking about Windows 8, Windows 8 comes with something called
"Defender." And guess what? It is both an anti-spyware and an anti-virus
program. It can pretty much stand on its own.

It is effectively "Microsoft Security Essentials" with a different name.

Microsoft Security Essentials

What I typically recommend for people in your situation (with your Windows 7
machine) is to download and install Microsoft Security Essentials.

That will automatically disable Windows Defender. It knows that Defender is
going to be there; it knows that Defender is no longer necessary because
Microsoft Security Essentials contains all of that functionality plus
anti-virus.

It's a good replacement for Defender, and it will handle it
transparently.

Duplicate malware programs

Now, as for the other anti-malware programs that you're talking about:
Norton and AVG and so forth?

I typically don't recommend that people need all of them. I think
one good solution is a great place to be. Microsoft Security Essentials is the
solution that I typically recommend for people - and it's the solution I use
myself.

Now, if you want to have Norton or AVG or something else on your machine,
typically it's OK to have them there.

Clashing real-time scans

What's most important is that you not have any of their real-time scanning
functions enabled.

It's not the presence of duplicate software that causes the
problem, it's the attempt of more than one anti-malware product trying to do
real-time scanning at the same time. That's when they can come into
conflict.

This could do two things:

1. It can cause false positives (where they'll both be complaining, or one or
   the other will be complaining about a problem that really isn't there);

2. Or worse, they can interfere with each other's ability to detect malware -
   and malware will go undetected.

So, if you have those tools there, they're fine. You can have them. They're
good for on-demand scans. But any of the automatic stuff? I would make serious
attempts to be sure you've got them completely disabled.

My most serious attempt is to not even bother having them on the
machine!

Microsoft Security Essentials, or AVG, or Norton? Just one of those
would be a fine solution to getting your machine protected. I happen to
recommend Microsoft Security Essentials.

Then, later, if and when you run into a problem, then you can take a look at
saying, "OK, fine. I've got some malware on my machine somehow. Let's get an
additional program or two to scan the machine to clean it up."

Those would be "on-demand" scans - without doing the real-time scanning that
we know can cause a problem.

Anti-virus AND anti-spyware

So, ultimately, Microsoft Security Essentials will transparently replace
Defender, which is exactly what you want.

Regardless of whether you use Microsoft Security Essentials or not, I
recommend that you have one good anti-malware package (Microsoft Security
Essentials or AVG or any of a number of others) to keep your machine
protected.

You do not need to load up on multiple anti-malware tools at once. It will
slow down your machine and potentially cause you a lot of false positives or
worse - missed detection.

(Transcript lightly edited for readability.)