Modern malware rarely announces itself with a skull on your screen. It mines, spies, and waits quietly — which is why the signs are subtle and easy to blame on “the computer just being old.” Here are the ten symptoms that actually matter, roughly in order of how often we see them, and the first thing to do about each.
The ten signs
1. The fans spin at full speed while you’re doing nothing. Cryptominers love idle CPUs. Open Task Manager (Ctrl+Shift+Esc) or Activity Monitor and look for unfamiliar processes pinning the CPU or GPU.
2. Your browser’s homepage or search engine changed itself. That’s a browser hijacker. Check your browser’s extensions list first — remove anything you didn’t install, then reset search settings.
3. Ads appear where ads shouldn’t be — on your desktop, or injected into sites that normally have none. Classic adware; run a reputable on-demand scanner.
4. Friends receive messages you never sent. Your email or social account may be compromised rather than your machine — change that password from a different device and enable two-factor authentication before anything else.
5. Your antivirus or Windows Defender is mysteriously off and won’t turn back on. Malware disables defences first. Boot into safe mode and scan from there.
6. New toolbars, apps or icons you never installed. Uninstall via system settings, not by deleting shortcuts — then scan, because bundled installers rarely travel alone.
7. Constant browser redirects. You click one link and land somewhere else twice. Check extensions, then your system’s proxy and DNS settings.
8. Unexplained data usage or network activity. Spyware phones home. Your router’s traffic page or a network monitor will show which device — and which process — is talking.
9. Files encrypted or a ransom note. Disconnect from the network immediately, don’t pay, don’t reboot repeatedly, and restore from backup after a clean reinstall.
10. Passwords stop working. If accounts lock you out and recovery emails you never requested arrive, assume credential theft: from a known-clean device, change passwords starting with email and banking.
If you confirm an infection
Scan with a second opinion tool (not just the antivirus that missed it), update the operating system, and change important passwords afterwards from a clean device. If ransomware or a banking trojan was involved, a full reinstall is the only answer you can trust. Slowness alone isn’t proof of malware, though — see our guide to why your computer is really slow, and check whether your accounts appeared in a breach with our data breach guide.
