Your computer was fine last month. Now it’s sluggish, pop-ups appear from nowhere, and your fan runs constantly even when you’re doing nothing. Is it just age, or has your computer caught something?

Malware in 2026 is sneakier than the old “YOUR COMPUTER HAS A VIRUS!!!” pop-ups. Modern malware wants to stay hidden — mining crypto with your processor, logging your keystrokes, or quietly stealing browser data. Here’s how to tell if your computer is infected and what to do about it.

The Classic Signs of Infection

  • Sudden, unexplained slowness. If performance fell off a cliff without a clear cause (no new software, no full drive), something may be consuming resources in the background. Check Task Manager / Activity Monitor for processes eating CPU that you don’t recognize.
  • Pop-ups and browser redirects. Ads appearing outside your browser, your homepage changed without permission, searches redirecting through sketchy sites — textbook adware/browser hijacker behavior.
  • New toolbars, extensions, or programs you didn’t install. Check your browser extensions and installed programs list. Anything you don’t recognize that appeared recently is suspect.
  • Friends receiving spam from your accounts. Email or social accounts sending junk you didn’t write means credentials are compromised — possibly via a keylogger or info-stealer on your machine.
  • Disabled security software. If your antivirus turned itself off and won’t turn back on, that’s malware fighting back. Take it seriously.
  • Unusual network activity. The hard drive light thrashing or network activity spiking when you’re doing nothing. (Also check which apps are using your data — on mobile, the same principle applies.)
  • Ransom notes or locked files. The nightmare scenario: ransomware. Files renamed with weird extensions and a demand for payment. Do not pay — it funds criminals and often doesn’t restore your files.
  • Camera or microphone activating unexpectedly. The little light flickering on when you’re not in a call is worth investigating immediately.

Signs It’s Probably NOT a Virus

To avoid panic: slow boot times alone usually mean too many startup programs or an old hard drive (see why your computer boots slowly). A hot laptop usually means dust (see laptop overheating fixes). Occasional crashes are often driver issues. Malware is one possible cause of slowness, not the default explanation.

What to Do If You Suspect Infection

  1. Disconnect from the internet — unplug ethernet or turn off Wi-Fi. This stops data theft and prevents the malware from calling home or spreading.
  2. Don’t log into anything sensitive. No banking, no email — assume keystrokes may be captured until you’re clean.
  3. Boot into Safe Mode (Windows: hold Shift while restarting → Troubleshoot → Startup Settings; Mac: hold Shift during boot). Safe Mode loads minimal software, which often prevents the malware from running.
  4. Run a full scan with Windows Defender (genuinely good now) or Malwarebytes Free. Let it complete — quick scans miss things.
  5. Remove what it finds, then run a second opinion scan with a different tool (ESET Online Scanner is free and excellent).
  6. Check browser extensions and reset your browser if hijacking persists — Chrome/Firefox/Edge all have a “reset settings” option that strips malicious extensions.
  7. Change your passwords — from a clean device — starting with email and banking. If a keylogger was present, assume credentials were captured. Then enable two-factor authentication everywhere.

The Nuclear Option

If scans find deeply embedded malware (rootkits) or ransomware encrypted your files: back up your data files only (documents, photos — not programs), then wipe and reinstall the OS completely. It’s the only way to be certain. Yes, it’s a hassle. It’s also the only guaranteed clean slate.

How You Probably Got It (So It Doesn’t Happen Again)

  • Fake downloads: “free” versions of paid software, game cheats, and “cracked” apps are the #1 infection vector. If you didn’t pay for it and it’s not open source, assume it’s malware.
  • Phishing attachments: the “invoice” or “delivery notice” you opened. When in doubt, don’t.
  • Malicious ads: even legitimate sites occasionally serve bad ads. An ad blocker (uBlock Origin) is legitimate security software at this point.
  • Outdated software: unpatched browsers, Office, and operating systems have known holes. Update promptly.
  • USB drives: found drives and borrowed drives. Don’t plug in mystery USB sticks.

Staying Clean Going Forward

  • Keep your OS and browser updated — automatic updates on, always
  • Use Windows Defender (it’s enough for most people) or one reputable antivirus — never two. Our roundup of free antivirus options for Windows covers the best choices.
  • Use an ad blocker and a password manager
  • Back up regularly — ransomware is a nuisance instead of a catastrophe when your files exist elsewhere
  • Be skeptical of urgency: “act now,” “your account will be closed,” “free download” — malware’s favorite words

The FTC’s malware guidance stays current on what’s circulating and is worth a periodic skim.

Frequently Asked Questions

Can Macs and iPhones get viruses?
Yes — the “Macs don’t get viruses” era ended years ago. Mac malware is less common than Windows malware (smaller target), but it exists and is growing: adware, info-stealers, and even ransomware have Mac variants. iPhones are much harder to infect (sandboxed apps, no sideloading outside the EU), but not immune — especially to phishing and malicious profiles. “Less targeted” never meant “invulnerable.”

Is Windows Defender enough, or do I need paid antivirus?
For most careful users, Defender plus smart habits is genuinely sufficient — it scores alongside paid products in independent tests. Add Malwarebytes Free as an on-demand second opinion and uBlock Origin in your browser, and you’re well protected for $0. Paid antivirus makes sense for high-risk users (kids, elderly relatives who click everything) or if you want the bundled extras (VPN, identity monitoring). Our free antivirus roundup compares the options.

How did I get a virus if I didn’t download anything?
Drive-by downloads from compromised ads (malvertising) can infect through the browser alone — no download click needed. Outdated software with known vulnerabilities is the other silent vector: an unpatched browser or Office install is an open door. This is why automatic updates and an ad blocker are security essentials, not nice-to-haves. “I didn’t click anything” is compatible with infection.

Should I pay if I get ransomware?
No — don’t pay. Payment funds criminal operations, marks you as a payer (inviting repeat attacks), and frequently doesn’t restore your files anyway (many ransomware strains are buggy). Instead: disconnect from the internet, identify the strain (nomoreransom.org can help), restore from backups, and in the worst case, wipe and reinstall. The real lesson is backups — ransomware against backed-up files is an afternoon’s inconvenience instead of a catastrophe.

The Bottom Line

Unexplained slowness plus pop-ups, mystery programs, disabled security, or spam from your accounts — that’s the pattern that says infection. Disconnect, Safe Mode, full scans from two tools, then change passwords from a clean device. And going forward: update everything, block ads, back up, and treat “free” downloads of paid software as the trap they are. An ounce of skepticism beats a pound of antivirus.