How Do I Make Sure Malware is Gone?

With preparation, you can. Without? Not so much.

You don’t.

I hate to say it, but there’s an important adage that everyone needs to understand:

Once infected with malware, it’s not your computer anymore.

And that holds true even after you believe you’ve removed the malware.

That’s not to say there isn’t hope of recovery, but it does point out the seriousness of the situation.

Making sure malware is gone

It’s nearly impossible to be certain that malware is gone. Most scans catch most malware, but nothing guarantees removal except restoring a pre-infection backup or wiping and reinstalling everything. Regular image backups make this easy. Prevention through safe internet habits and backups is the best defense against these scenarios.

It’s not your computer anymore

That’s a strong statement, and I want to clarify what I mean by that.

Once on your computer or other device, malicious software can do anything it wants to. Not all malware does — and indeed, not all malware can — but there is malware that can, will, and does take over your machine in ways you might not expect and in ways that are difficult, if not impossible, to detect.

You don’t want to place bets on whether you have the kind that doesn’t take over your machine or the kind that does. They may look the same as you use your machine. The second, however, could lay in wait to do something nasty, it could be silently doing something nasty you might not notice (like collecting keystrokes), or it might cause unexpected behavior, like system slowdowns as your machine turns into a part of a botnet.

Once it’s on your machine, malware can do whatever it wants. That means it’s become the malware’s computer, not yours.

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What about scanning?

The most common advice about removing malware is to scan. Specifically:

• Update your security software.
• Scan with your security software.
• Scan again with your security software.
• Try an additional scan with other security software.

I’ve seen people repeat that last step until their machine is chock full of security packages that end up doing more harm than good.

Even after all that, there’s no guarantee that malware won’t remain.

To be clear, most malware will be caught, flagged, and removed. The tools do work and generally work well. It’s just that nothing’s perfect. All tools miss things.

And some malware tries very hard to be the malware that’s missed.

Running those scans is enough 991 times out of 100. It’s that 1% left that’s of concern. Remember, the question here is how to make sure that the malware is gone.

You want a guarantee.

Guarantee #1: Fairly easy

You can remove malware and be sure you’ve removed it by restoring your machine to an image backup taken prior to the malware’s arrival. After that, avoid doing whatever allowed the malware in to begin with.

This is one of the two most important things image backups are for.2 It’s relatively easy, it’s relatively fast, and it’s guaranteed.

It’s also something you must have been doing before needing it. This is why I so strongly recommend daily image backups.3

A little preparation goes a long, long way.

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Guarantee #2: Nuclear

If you haven’t been backing up regularly, the only way to know you’ve removed malware is to erase everything. “Everything” would, by definition, include the malware. Unfortunately, it also means erasing everything else, like your data, installed programs, and the operating system.

The process looks like this:

• Back up your existing hard drive (so as not to lose anything important).
• Reinstall Windows from scratch.
• Reinstall applications from scratch.
• Restore your data from your backup or elsewhere.

All that just to get rid of malware?

No. All that to make certain you got rid of malware.

Anything less is a compromise

I’m not suggesting you drop everything at the first sign of malware and reinstall everything from scratch. (I am, of course, suggesting you begin backing up regularly.)

Sometimes 99% certainty is enough. Sometimes 99% is enough to carry on unless there are other signs that you’re part of the 1% (like whatever caused you to discover you had malware in the first place) and need to take more drastic measures.

But if you want or need a guarantee, you’ve got two options:

1. Restore a backup.
2. Reinstall from scratch.

A note about BIOS/UEFI compromise

Whenever I talk about recovering from malware and how a full format and reinstall are the only guarantee, I get push-back that they’re not. And it’s true that if your BIOS or UEFI has been compromised, even the nuclear option won’t help, since it doesn’t touch them.

To begin with, there’s no such thing as perfect security. None. It’s a spectrum. The goal is to be on the “as safe as you can be” part of the spectrum.

Second: just because something might be possible doesn’t mean it’s happening to you or that it’s likely to happen to you. BIOS/UEFI compromise is rare4. There are plenty of more common malicious approaches that represent a much greater risk, all of which are covered by the process above.

Put another way: I don’t worry about BIOS/UEFI attacks specifically. I follow safe security practices that keep me safe from all malware, whether it’s a keylogger, ransomware, a bot, or something else entirely, such as some kind of BIOS/UEFI compromise.

I recommend you take the same approach.

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