Vet your visitors before inviting them in.
I was somewhat taken aback by this question. It’s a perfectly good question, and one that more people should be asking more often.
My reaction was due to the lack of a good answer.
It turns out it’s fairly difficult to tell whether or not a download is about to play havoc with your system, particularly before you download it.
But it’s getting better.
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In order to be scannable by your anti-malware tool, a questionable file must be able to be read by the tool. That means the file needs to be in the process of downloading, or already be downloaded, to your computer. The best way to avoid a problem is to only download from sites and companies you trust, never download illegal software, scan your downloads as soon as you can, and of course back up regularly in case the worst happens. Always be skeptical.
What anti-malware tools do
Anti-malware scanners look at the contents of the files on your system to see if they have what appear to be viruses or not. The files don’t have to be installed or running; they just have to be accessible to the scanner. You can and should scan that file before you run it.
But the files do have to be on your system, or (in some rare cases) in the process of being downloaded.
Before you download? There’s effectively no solution. You have to download it in order to be able to scan it yourself.
What to do?
So, what do you do? What do I do, for that matter?
Our best defense is to fall back on common sense and best practices for avoiding malware in the first place.
- Only download from sites you trust. Knowing who to trust is a difficult problem. My recommendation is to avoid downloading from third parties. If a piece of software is created by XYZ corporation, download it directly from XYZ corporation’s website. If it’s available directly from the creator, there’s no reason to get it anywhere else. Avoid download sites if at all possible.
- Only download from companies you trust. Even if you do download directly from the creator’s website, not all creators are ethical or above-board. If you’ve not heard of the company before, it’s worth a search to see if other people have experienced problems. A lot of free software is “free” because it’s loaded with PUPs, for example. It might be legal, but it can certainly be annoying.
- Never download illegal software. You shouldn’t anyway — because it’s illegal — but even if that doesn’t stop you, the risks should. Illegal software is lucrative because it’s free or dirt cheap. Malware creators know this and often use it as an opportunity to distribute their wares.
- Scan your download. This is the easy one. Anti-malware tools can easily and quickly scan a downloaded file and tell you whether or not it contains any known viruses. Make sure to keep your virus program, and its database, up to date.
- Back up. Even though you may trust what you’ve just downloaded, prepare for the worst anyway. Assume that what you’re about to install will cause your machine to crash and become unbootable. Would you lose important data? Then you better make sure it’s backed up first.
It’s getting a little better
I recently downloaded an update to a (legitimate) program I use, and received the following warning:
That was Windows Defender warning me that it didn’t “recognize” the application I was about to run.
That doesn’t mean it’s malware or that there’s anything wrong with it at all — it just means that Windows Defender (meaning Microsoft) was unfamiliar with the vendor, or perhaps the software wasn’t digitally signed. All it really means is to take a breath and consider whether you recognize and trust the application and its vendor. (In this case, you can click “More info” which will expose a “Run anyway” button, which is what I used.)
Other security tools use a more aggressive form of application white-listing, meaning only applications that have been somehow pre-vetted and confirmed not to be malicious are allowed to run.
The best advice? Skepticism
In some ways, it’s not surprising malware is as common as it is. Absolute prevention is difficult at best. Even with the best tools, people often actively circumventing warnings and other blocks to download whatever they (apparently desperately) want.
Most remedies are nothing more than damage control once malware arrives.
The best defense is you. You are both the weakest link and the strongest hope for your own security. Be skeptical, take the time, and make the effort to choose your downloads with care.
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