How to Check if Your Windows PC Has Been Compromised

Not every infection announces itself with a ransom note or a crashed system. Many modern threats are designed to stay quiet — stealing data, mining cryptocurrency, or sitting as a foothold for later use, all while trying not to be noticed. Knowing the subtle warning signs, and how to check for them, is a skill worth having.

Behavioral Warning Signs

• Unusual slowness, especially fans running at full speed when you’re not doing anything demanding — could indicate background processes like cryptominers.
• Programs opening or closing on their own, or your browser homepage/search engine changing without your input.
• New toolbars, extensions, or icons you didn’t install.
• Unexpected pop-ups, especially ones claiming your PC is infected and urging you to call a number or download “antivirus” software — this itself is often the scam.
• Friends receiving messages or emails from you that you didn’t send.
• Webcam light turning on without you using it.
• Unusually high network activity when you’re not actively using the internet.

None of these alone is proof of compromise, but more than one together is worth investigating.

Step-by-Step Check

1. Run a full scan with Windows Security Search “Windows Security” in the Start menu > Virus & threat protection > Scan options > Full scan. This is slower than a quick scan but checks every file, not just common infection points.

2. Check Task Manager for unfamiliar processes Press Ctrl + Shift + Esc. Look through the Processes tab for anything you don’t recognize, especially items using high CPU or network activity. Right-click to search online for unfamiliar process names before assuming the worst — many legitimate background processes have unintuitive names.

3. Review installed programs Settings > Apps > Installed apps. Sort by install date if possible, and look for anything you don’t remember installing — this is a common sign of bundled malware that rode in with another download.

4. Check startup programs Task Manager > Startup apps tab. Malware frequently adds itself here to persist across reboots. Disable anything unfamiliar.

5. Check browser extensions In Chrome/Edge: Settings > Extensions. Remove anything you don’t remember installing — browser extensions are a common vector for credential theft and ad injection.

6. Check for unauthorized account access If you suspect your Microsoft account specifically, go to account.microsoft.com and review “Sign-in activity” for unfamiliar locations or devices.

7. Run a second opinion scan Tools like Malwarebytes (free version) use different detection methods than Windows Defender and can catch things the built-in scanner misses, particularly adware and potentially unwanted programs.

If You Confirm an Infection

1. Disconnect from the internet/Wi-Fi to stop any potential data exfiltration or remote control.
2. Run a full scan and follow the removal prompts.
3. Change your passwords after the device is confirmed clean, not before — changing them on an infected machine can hand the new password straight to the attacker.
4. Enable multi-factor authentication on any accounts you access from that device, if not already on.
5. For serious or persistent infections, a clean Windows reinstall is sometimes the most reliable option — some malware is specifically designed to survive removal attempts.

Quick Checklist

• Full scan run with Windows Security (not just a quick scan)
• Task Manager reviewed for unfamiliar high-usage processes
• Installed apps list checked for anything unrecognized
• Startup programs and browser extensions reviewed
• Second-opinion scan run with a different tool (e.g., Malwarebytes)

The Bottom Line

Most compromises are more subtle than people expect, which is exactly why they go unnoticed for so long. Making a habit of periodic checks — Task Manager, startup programs, browser extensions — takes a few minutes and dramatically shortens the time between infection and detection, which is often the single biggest factor in how much damage ends up being done.