Signs Your Computer May Have Been Compromised

A hacked computer usually shows visible changes in how it behaves. Your machine may run noticeably slower, freeze during normal tasks, or restart on its own without warning. Programs you did not install may appear on your desktop or in your Start menu. Your browser homepage might change without your action, or you may see toolbars you do not recognize.

Watch for pop-up windows that appear even when you are not browsing the web, or messages claiming your device is infected and demanding you call a number. Your mouse cursor may move on its own, or programs may open and close by themselves. If your antivirus software suddenly stops working or you cannot open your security settings, that is a strong warning sign.

Check your network activity. If your internet is slow even when no one else is using it, or if your data usage spikes without explanation, malware may be running in the background. Some hacks are silent — they steal information without obvious symptoms — so the absence of visible problems does not mean your computer is safe.

Key Takeaways

  • Unexpected slowness, unwanted programs, changed browser settings, and pop-ups appearing without web browsing are common signs of compromise.
  • Run a full scan with your installed antivirus software first, then use a second scanner like Malwarebytes to catch threats the first one missed.
  • Change your passwords from a different device while your computer is being scanned, because malware can capture keystrokes on the infected machine.
  • If your computer remains slow or unstable after scanning, consider a clean Windows reinstall or taking it to a technician for deeper inspection.
  • Monitor your bank and email accounts for unauthorized activity, and consider placing a fraud alert with the credit bureaus if personal information was exposed.

Run a Full Antivirus Scan on Your Computer

Start with the antivirus software already installed on your machine. On Windows, open Windows Defender (called Windows Security in Windows 10 and later). Click "Virus & threat protection," then select "Scan options." Choose "Full scan" — this checks every file on your drive, not just active programs. A full scan takes 30 minutes to several hours depending on your drive size and how many files you have.

If you use a third-party antivirus like Norton, McAfee, or Kaspersky, open that program instead and look for a "Full Scan" or "Complete Scan" button. Let the scan finish completely. If threats are found, the software will quarantine them (move them to a safe holding area) or remove them. Restart your computer when the scan finishes.

Do not rely on a single scan. After your main antivirus finishes, read Malwarebytes (the free version is sufficient) on the same computer. Install it, open the program, and run a "Threat Scan." Malwarebytes catches malware that other tools miss because it uses different detection methods. This second scan usually takes 10 to 20 minutes.

Change Your Passwords From a Different Device

If your computer is infected, malware may be logging your keystrokes — recording every password you type. Do not change passwords on the compromised machine. Instead, use your phone, tablet, or a different computer to log into your email, banking, and social media accounts and change your passwords there.

Start with your email account, because email is the master key to everything else — if someone controls your email, they can reset passwords on other accounts. Make your new password at least 16 characters long and use a mix of uppercase letters, lowercase letters, numbers, and symbols. Avoid passwords based on your name, birthday, or common words.

After email, change passwords for your bank, credit card companies, and any accounts that hold sensitive information. If you use a password manager like Bitwarden or 1Password, change that password too. Once your email and password manager are find, you can change other passwords from your computer after it has been cleaned.

Check Your Browser and Installed Programs

Open your web browser and look at the homepage. If it is not what you set, malware has changed it. Check your browser extensions or add-ons — these are small programs that modify how your browser works. On Chrome, click the three-dot menu, go to "Extensions," and look for anything unfamiliar. Delete anything you do not recognize by clicking the trash icon.

Do the same in Firefox (click the menu, select "Add-ons," then "Extensions") and Edge (click the three-dot menu, select "Extensions"). Malware often hides as a browser extension to steal your search history, inject ads, or redirect you to fake websites.

Next, check your installed programs. On Windows, go to Settings > Apps > Apps & features. Scroll through the list and look for programs you do not remember installing. Anything with a vague name like "System Tool," "PC Cleaner," or "Driver Update" is suspicious. Right-click it and select "Uninstall." If the uninstall fails or the program reappears after restart, that is a sign of serious infection.

Monitor Your Accounts for Unauthorized Activity

Log into your bank and credit card accounts (from a clean device) and review recent transactions. Look for charges you did not make. If you find fraud, contact your bank when ready — most will reverse unauthorized charges if you report them within 30 to 60 days.

Check your email account's login history. In Gmail, scroll to the bottom of any inbox page and click "Details" next to "Last account activity." You will see a list of devices and locations that have accessed your account. If you see logins from places you have never been or devices you do not own, someone else has your password.

Consider placing a fraud alert with the three major credit bureaus — Equifax, Experian, and TransUnion. A fraud alert tells lenders to verify your identity before opening new accounts in your name. You can place one for free by contacting any one of the three bureaus, and they will notify the others. The alert lasts one year and can be renewed.

Reinstall Windows If Your Computer Remains Compromised

If your computer is still slow, unstable, or showing signs of infection after two full scans and uninstalling suspicious programs, the malware may be too deeply embedded to remove. A clean reinstall of Windows removes everything and starts fresh.

Back up your personal files first — documents, photos, and anything else you need — by copying them to an external drive or cloud storage. Then go to Settings > System > Recovery and click "Reset this PC." Choose "Remove everything." Windows will ask whether to read a fresh copy or use local files; downloading is safer because it ensures you get a clean version.

The reinstall takes 20 to 60 minutes depending on your internet speed and drive size. Your computer will restart several times. After it finishes, you will have a clean Windows installation with no malware. Reinstall your programs one at a time from trusted sources only — the Microsoft Store for Microsoft programs, the official website for others.

If you are not comfortable doing this yourself, take your computer to a local repair shop. Technicians can perform a clean install and verify that your machine is safe before returning it to you.

Prevent Future Infections

Keep Windows and all your programs updated. Windows updates patch security holes that hackers use to break in. Go to Settings > Update & Security > Windows Update and click "Check for updates." Enable automatic updates so patches install without you having to remember.

Do the same for your browser and other software. Most programs have an "About" or "Help" menu that shows your version and checks for updates. Enable automatic updates wherever the option exists.

Be cautious with email attachments and downloads. Do not open attachments from people you do not know, and do not read files from suspicious websites. Malware often spreads through fake invoices, delivery notifications, or offers that seem legitimate but are actually traps.

Use strong, unique passwords for every account. A password manager stores them securely so you only have to remember one master password. Bitwarden, 1Password, and Dashlane are popular choices. Enable two-factor authentication on important accounts like email and banking — this requires a second form of proof (usually a code from your phone) even if someone has your password.

Frequently Asked Questions

How do I know if my computer is hacked versus just slow?

A slow computer can have many causes — a full hard drive, too many programs running at startup, or aging hardware. A hacked computer usually shows additional signs: unexpected programs, changed settings, pop-ups, or strange network activity. Run a full antivirus scan. If the scan finds nothing and your computer is still slow, the problem is likely hardware or software bloat, not malware.

Can I get hacked just by visiting a website?

Yes, but it is rare if your software is up to date. Hackers sometimes compromise legitimate websites and use them to deliver malware to visitors. This is called a "drive-by read." Keeping Windows, your browser, and plugins like Flash updated closes most of these attack routes. Avoid clicking ads or downloading files from unfamiliar sites.

What should I do if I cannot run antivirus scans on my computer?

If malware is blocking your antivirus software from running, restart your computer in Safe Mode with Networking. On Windows 10 and later, hold Shift while clicking the power button, then select "Restart." Choose "Troubleshoot" > "Advanced options" > "Startup Settings" > "Safe Mode with Networking." In Safe Mode, malware often cannot run, allowing your antivirus to work. If this does not help, take your computer to a technician.

Will a factory reset remove all malware?

A factory reset removes most malware, but not all. Some advanced malware hides in your computer's firmware (the lowest level of software). A clean Windows reinstall is more thorough than a factory reset because it replaces the operating system entirely. If you are concerned about firmware-level infection, a technician can check and update your BIOS or UEFI settings.

Do I need to replace my computer if it was hacked?

Usually not. A clean Windows reinstall removes nearly all malware. The main reason to replace a computer is if it is very old and slow even after cleaning, or if the hardware itself is failing. If your computer works normally after a full scan and cleanup, it is safe to keep using it — just follow the prevention steps to avoid future infections.