Does Turning a Computer Off at Night Keep It Safer From Hackers?

Technically, yes, a teeny tiny bit. Pragmatically? It’s not worth considering.

My article on turning your computer off overnight frequently prompts people to ask if (or emphatically state that) turning off your computer keeps it safer from being hacked.

While the answer is “yes” if you want to be pedantic about it, the more practical answer is “no”.

Let me explain how you’re protected by 1) your computer and 2) yourself.

Turning off the computer for hackers

Turning off your computer overnight doesn’t significantly increase safety from hacking. Your NAT router already blocks unsolicited connections. Malware risks arise from user actions, like opening unsafe attachments. Focus on practicing safe computing and keeping your system malware-free. Leave your computer on or off overnight based on convenience and power concerns rather than worries about hacking.

You are protected by your router

Here’s the thing: a random program out on the internet cannot connect to your computer on its own. Period. A side effect of the way your router handles internet addressing — sharing your internet IP address among all the devices you have connected — prevents unsolicited incoming connections.

A computer connected directly to the internet1 is at high risk. There are stories of such computers being infected with malware within moments of being connected. It’s one reason I say we are all under constant attack.

A computer behind a Network Address Translation (NAT) router is safe from these incursions. Period. Day or night. Running or not. Chances are you already have one, and if you have more than one device connected to the internet, you almost certainly do.

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Things that look like incoming connections aren’t

You might be wondering, then, how tools like messaging programs, file sync programs, or even email programs on your computer get notified when there’s something they need to do. Someone’s trying to send you a message, a file has been updated in the cloud and needs to be downloaded, an email has been sent to you, and so on, and your computer needs to act on it.

Those services are not connecting to your computer.

They use a “man on the inside”: the software installed on your machine that deals with those services.

Your computer initiates the conversation by reaching out to the messaging service, the cloud storage service, the email service, or whatever else. It might periodically check if there’s something new (like email), or it might have created a conversation when the program was first run on your PC and kept that conversation going continuously so the app on your computer and the service online can talk to each other when needed.

But the connection is never2 initiated from the internet. It’s always your computer reaching out.

Always.

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You’re protected by… you

If the only things that show up on your computer are things the computer asks for, that means these things come from one of exactly two places:

• The software running on your machine. (Windows updates, mail programs, cloud sync programs, and so on.)
• You.

The second is where malware comes from. In fact, the most common cause of malware infections is probably people opening attachments they shouldn’t.

You, of course, practice safe computing. You know not to do that.

Pedants’ corner

There is a sliver of accuracy regarding turning off your computer and how it keeps you “safer”. When you turn it off:

1. You’re not using it. If you’re not using it, you won’t open malicious attachments or do other things that result in your machine being compromised.
2. Malware already on your machine will not run.

It’s the second one that causes most people the most concern. If your machine is infected with malware and software on your machine can “reach out” and download more malicious stuff, then turning off the machine will prevent an existing infection from getting worse.

But for that to matter means you already have malware on your machine! Turning off your machine won’t do anything about that; it’ll still be there when you turn it back on. The very thing you’re trying to prevent by turning off the machine has already affected you.

Focus instead on keeping yourself malware-free to begin with.

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