Is Your Computer Running Slow? It Might Be Malware — Here's How to Check

Last updated: 2026-06-24

The short answer: A computer that suddenly slows down — especially one that used to run fine — is one of the top warning signs that malware is running quietly in the background. The good news: Windows and Mac both have free built-in tools that can scan your computer in under 15 minutes. Here's exactly what to do.

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You've had your computer for a few years and it's always worked fine. Then one day it starts taking forever to start up. Web pages load slowly. Sometimes the mouse freezes for a few seconds for no reason.

Your first thought is probably: it's just getting old.

That's sometimes true. But a sudden change in speed — especially if nothing else has changed — is worth paying attention to. It's one of the most common warning signs that something unwanted has found its way onto your computer.

And unlike a hardware problem that just slows things down, malware is often doing something much worse in the background: quietly sending your passwords, bank account numbers, or personal information to strangers.

This guide will help you figure out what's actually going on — and what to do about it.

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What Is Malware, and Why Does It Slow Down Your Computer?

"Malware" is short for malicious software. It's any program that got onto your computer without your permission and is working against you instead of for you.

There are several kinds:

• Spyware watches what you type — especially passwords and credit card numbers — and secretly sends that information elsewhere.
• Adware floods your screen with pop-up ads and tracks your browsing habits.
• Ransomware locks all your files and demands money to unlock them.
• Cryptominers secretly use your computer's processing power to earn digital currency for someone else.
• Viruses attach to files and spread when you share those files with others.

When malware runs on your computer, it uses your machine's resources — memory, processing power, internet connection — to do its work. That's why your computer slows down. It's not just running your programs anymore. It's running theirs too.

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Normal Slowness vs. Malware Slowness: How to Tell the Difference

Not every slow computer has malware. Age, too many programs, and outdated software can all cause slowdowns. But certain patterns suggest something more suspicious.

Signs that point toward normal wear or overload:

• Your computer has been slow for years, not just recently
• It slows down when you have many browser tabs or programs open at once
• It gets faster after you restart it
• Slowdowns happen during demanding tasks like streaming video

Signs that suggest malware:

• The slowdown happened suddenly — seemingly overnight
• Your computer is slow right after startup, even with nothing open
• Pop-up ads are appearing that you've never seen before, even when your browser is closed
• Your browser's homepage changed to something you didn't set
• There are programs installed that you don't recognize
• Your internet usage is unusually high (your provider can tell you this)
• The computer's fan runs constantly at full speed even when you're doing nothing
• You're getting logged out of accounts unexpectedly, or receiving login alerts from unfamiliar locations

If you're seeing two or more items from that second list, a malware scan is a smart next step.

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Step 1: Use Your Computer's Built-In Security Tool

Before downloading anything, start with what you already have. Both Windows and Mac computers come with free, built-in security tools that are updated automatically.

On a Windows PC (Windows 10 or 11)

Windows comes with a program called Windows Security (also called Windows Defender). It's not just basic protection — it's a full antivirus and anti-malware tool.

Here's how to run a scan:

1. Click the Start button (the Windows logo in the lower-left corner of your screen)
2. Type Windows Security and click it when it appears
3. Click Virus & threat protection
4. Click Quick scan
5. Wait while Windows checks your computer — this usually takes 5 to 15 minutes
6. When it finishes, it will tell you if anything was found

If it finds something, follow the on-screen instructions. Windows Security handles most common threats automatically — you usually just click "Remove" or "Quarantine."

For a more thorough check, you can also run a Full scan from the same menu. This takes longer (sometimes an hour or more) but checks every file on your computer. It's worth doing if you're seriously concerned.

On a Mac

Macs have strong built-in protections that run automatically in the background, including a system called XProtect that Apple updates regularly. You don't run it manually — it works silently on its own.

To review your Mac's security settings:

1. Click the Apple logo in the top-left corner
2. Click System Settings (or System Preferences on older Macs)
3. Click Privacy & Security
4. Make sure your Mac is set to allow apps only from the App Store and identified developers

If you're still concerned, the free version of Malwarebytes for Mac (described in Step 2 below) is the most recommended second-opinion tool for Mac users.

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Step 2: Run a Free Second-Opinion Scan

Think of this like getting a second opinion from a doctor. Your built-in tools are good, but a second scanner can catch things the first one missed.

Malwarebytes is a trusted, free tool for exactly this purpose. It's been around for over 15 years and is widely recommended by security experts and AARP as a legitimate, safe download. The free version lets you scan and remove whatever it finds — no payment required.

How to get it:

1. Open your web browser and type malwarebytes.com directly into the address bar — don't click a link in an email or pop-up ad to get here
2. Download the free version and open the file when it finishes downloading
3. Follow the simple installation steps
4. Once installed, click Scan Now
5. Malwarebytes will review your computer and list anything suspicious it finds

If it finds items to remove, click Quarantine, then restart your computer when prompted.

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What to Do If Malware Was Found

First: don't panic. Finding malware is actually good news in one sense — now you know, and you can fix it. Many people have malware on their computers for months without realizing it, and they're in a much worse position.

Here's what to do immediately after removing it:

Change your important passwords. Start with your email (especially Gmail, Yahoo Mail, or Outlook), then your online banking and investment accounts, then any shopping sites where your credit card is saved. If possible, do this from a different device — your smartphone or tablet — just to be safe. If malware was running while you typed those passwords, they may have been captured.

Check your bank and credit card statements. Look for any charges you don't recognize, even small ones. Scammers often test with a tiny charge — $1 or $2 — before making a larger one. Call your bank immediately if you see anything unfamiliar.

Check your email's Sent folder. Malware sometimes sends emails from your account to your entire contact list. If you see messages you didn't send, let your contacts know, and consider notifying your email provider.

Tell someone you trust. If you're unsure whether the situation is fully resolved, call a trusted family member or friend who's comfortable with technology. The AARP Fraud Watch Network also has a helpline (877-908-3360) staffed by people who help seniors navigate exactly this kind of situation.

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Why Malware Targets Seniors Specifically

You might wonder why your computer would be targeted. The answer is that you probably weren't singled out personally — but seniors as a group are high-value targets for cybercriminals for a few specific reasons.

Retirement savings. Adults 55 and older generally have more savings than younger people. Access to their financial accounts is more valuable.

Higher trust levels. Research consistently shows that many older adults are more likely to trust unexpected alerts, pop-ups, or calls from someone claiming to be from Microsoft, Medicare, or their bank. Scammers know this and design their tactics accordingly.

Less exposure to evolving scam tactics. Fake virus alerts, phishing emails, and remote access scams were designed specifically to fool people who didn't grow up learning to be skeptical of every online message.

This isn't a criticism — these tactics fool technology professionals too, when they're done well. Knowing the patterns is the best defense.

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Protect Your Identity After a Malware Infection

Here's something many people don't consider: just because the malware is gone doesn't mean the damage stops.

If malware was on your computer — even briefly — it may have already captured and transmitted your personal information. Passwords, credit card numbers, bank account details, or a Social Security number you typed while the malware was active could have been sent to someone else.

This is where identity monitoring becomes important. Instead of waiting to discover your identity was stolen months after the fact (when the damage is already done), a good identity monitoring service watches for warning signs on your behalf and alerts you immediately if something suspicious turns up.

Aura is one of the most comprehensive options available. It monitors:

• Your credit reports at all three bureaus (Equifax, Experian, TransUnion)
• Bank and financial accounts for suspicious activity
• Your Social Security number
• The dark web — underground sites where stolen personal information is bought and sold
• Your name appearing in public records in unexpected ways

If anything looks off, Aura sends you an alert right away so you can act before real damage is done. Aura also includes up to $1 million in identity theft insurance if you ever need legal or financial help recovering from fraud.

For anyone who has found malware on their computer — or suspects they might have at some point in the past — identity monitoring is the most important next step.

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Your Malware Response Checklist

Print this out and keep it somewhere handy:

• [ ] Computer suddenly slower than usual → run a scan
• [ ] Unexpected pop-up ads → run a scan
• [ ] Browser homepage changed without your doing → run a scan + change passwords
• [ ] New programs you didn't install → run a scan + check bank statements
• [ ] Scan found malware → change passwords from a different device
• [ ] Changed passwords → set up identity monitoring with Aura
• [ ] Using public Wi-Fi regularly → protect yourself with NordVPN

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The Bottom Line

A slow computer isn't always malware — but it's worth 15 minutes to find out. Windows and Mac both have free tools that make a scan easy, and the free version of Malwarebytes can catch what built-in tools miss.

If malware was on your computer, take the extra step of monitoring your identity. The damage from an infection doesn't always show up right away — sometimes it takes months, by which point criminals have already done real harm.

Going forward: healthy skepticism about unexpected pop-ups, emails, and phone calls — plus a VPN when using public Wi-Fi — are your two best defenses.

You don't have to be a tech expert to stay safe. You just have to take a few minutes when something seems off.

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