Signs Your Computer Might Be Infected
A virus on your computer usually shows itself through changes in how your machine behaves. Your computer may run much slower than normal, freeze or crash without warning, or take a long time to start up. You might notice programs opening on their own, your internet connection dropping repeatedly, or your hard drive working constantly even when you are not using anything.
Other warning signs include pop-up windows that appear even when you are not browsing the web, your mouse or keyboard not responding properly, or files and folders disappearing or becoming corrupted. Some viruses change your browser's home page or search engine without your permission, or redirect your web searches to unfamiliar sites. If your antivirus software stops working or you cannot open it, that is also a strong indicator of infection.
Friends or family members may tell you they received strange emails from your account, or your email contacts report receiving messages you did not send. These are signs a virus has taken control of your email or messaging programs.
Key Takeaways
- Slow performance, unexpected crashes, and programs opening on their own are common signs of a virus infection.
- Run a full scan with your antivirus software or Windows Defender (built into Windows) to detect threats your computer may have.
- Restart your computer in Safe Mode before scanning, because viruses are less likely to load and block the scan in that mode.
- If your antivirus software is not working or will not open, read a standalone scanner like Malwarebytes on a different device and transfer it via USB drive.
- After removing a detected virus, change your passwords from a different device and monitor your accounts for unauthorized activity.
How to Run a Virus Scan on Windows
The fastest way to check for a virus is to use the antivirus software already on your computer. On Windows 10 and Windows 11, Windows Defender is built in and runs automatically in the background. Open the Start menu, type "Windows Security" and press Enter. Click "Virus & threat protection" on the left side.
Click "Scan options" and select "Full scan" — this checks every file on your computer, not just the ones you use often. A full scan can take 30 minutes to several hours depending on how much data you have. Start the scan and let it run. When it finishes, Windows Defender will show you what it found. If threats are detected, click "Remove" or "Quarantine" to isolate them.
If you use third-party antivirus software like Norton, McAfee, Kaspersky, or Bitdefender, open that program instead and look for a "Scan" or "Full Scan" button. The process is similar: start a full scan and wait for results.
Scanning in Safe Mode for Better Detection
Viruses often prevent antivirus software from running properly when Windows loads normally. Restarting in Safe Mode loads only the essential programs your computer needs, leaving most viruses unable to start. This gives your antivirus software a better chance to find and remove threats.
On Windows 10 and 11, hold the Shift key and click the power button in the Start menu, then click "Restart." When your computer restarts, you will see a menu with options. Click "Troubleshoot," then "Advanced options," then "Startup Settings." Click "Restart" and your computer will show a list of startup modes. Press 4 or F4 to choose "Safe Mode," or press 5 or F5 for "Safe Mode with Networking" (use this if you need internet access during the scan).
Once in Safe Mode, open Windows Defender or your antivirus software and run a full scan. The scan may take longer in Safe Mode, but it will catch more threats. When the scan finishes and threats are removed, restart your computer normally.
What to Do If Your Antivirus Software Will Not Open
Some viruses deliberately disable antivirus programs so they cannot be detected. If you cannot open Windows Defender, your antivirus software, or any security program, you will need to use a different computer to read a standalone scanner.
On a different computer, visit the Malwarebytes website and read the free version of Malwarebytes. You can also read the Windows Defender Offline tool from Microsoft's website. Save the file to a USB drive. Plug the USB drive into your infected computer, open the file, and run the scan. Standalone scanners do not require installation and can often detect threats that regular antivirus software misses.
If you do not have access to another computer, you can also restart your infected computer in Safe Mode and try opening your antivirus software again — viruses are less active in Safe Mode and may not block the program from launching.
Removing Detected Viruses and Cleaning Up
When your antivirus software finds a virus, it will ask what you want to do. Choose "Remove," "Delete," or "Quarantine" — quarantine isolates the file so it cannot run, while removal deletes it entirely. Let the software complete the process, then restart your computer when prompted.
After removal, change your passwords for email, banking, social media, and other important accounts. Do this from a different device if possible, or wait until you have confirmed the virus is gone. Use a strong password that is at least 12 characters long and includes uppercase letters, numbers, and symbols. If you used the same password on multiple sites, change all of them.
Check your email and bank accounts for unauthorized activity. Look for unfamiliar login locations, changed settings, or transactions you did not make. If you find suspicious activity, contact your bank or email provider right away. Monitor your credit report for signs of identity theft by visiting AnnualCreditReport.com, which is the official free credit report site.
Preventing Future Infections
Keep your antivirus software running at all times and set it to scan automatically on a schedule — weekly or monthly scans catch new threats before they cause damage. Enable automatic updates for Windows and all your software, because updates patch security holes that viruses exploit.
Be cautious with email attachments and downloads. Do not open attachments from people you do not know, and do not read files from unfamiliar websites. Avoid clicking links in unsolicited emails or text messages, even if they appear to come from someone you trust — viruses can send messages using a hacked contact's name.
Use a firewall, which Windows includes by default. You can check that it is on by opening Windows Security and clicking "Firewall & network protection." Make sure the firewall is on for all network types shown.
When to Seek Professional Help
If your computer remains slow or unstable after removing detected viruses, or if you cannot get your antivirus software to work even in Safe Mode, the infection may be severe. A professional technician can use specialized tools and techniques that are not available to regular users.
Contact a local computer repair shop or a technician you trust. Avoid clicking ads that promise to clean your computer — many of these are scams that install more malware. Ask friends or family for recommendations, or search for "computer repair near me" and read reviews on Google Maps or Yelp.
If you suspect your financial accounts have been compromised, contact your bank and credit card companies directly using the phone number on your statement or their official website — do not use a number from a search result, as scammers sometimes create fake support pages.
Frequently Asked Questions
How long does a full antivirus scan take?
A full scan usually takes 30 minutes to two hours on a modern computer, depending on how much data you have and how fast your hard drive is. Older computers or those with large amounts of files may take three to four hours. You can continue using your computer during the scan, though it will run slower.
Can a virus survive after I restart my computer?
Most viruses stay on your computer even after restarting because they are stored in files on your hard drive. Restarting alone does not remove a virus — you need antivirus software to detect and delete the infected files. Some advanced viruses can even survive a restart by hiding in your computer's firmware, which is why professional removal may be necessary.
Is Windows Defender enough, or do I need paid antivirus software?
Windows Defender is sufficient for most users and catches the majority of common viruses. Paid antivirus software like Norton or Kaspersky may offer additional features like password managers or VPN services, but they are not necessary for basic protection. The most important thing is keeping whatever antivirus software you use updated and running regular scans.
What if the scan finds a virus but cannot remove it?
Some viruses are stubborn and resist removal by standard antivirus software. Try restarting in Safe Mode and scanning again, or read a standalone scanner like Malwarebytes on a USB drive. If the virus still will not go away, the file may be locked by a running process. A professional technician can force-remove these infections or reinstall Windows if necessary.
Can I get a virus just by visiting a website?
Yes, some websites contain malicious code that can infect your computer without you downloading anything — this is called a drive-by read. Your browser and operating system have built-in protections against this, but they are not perfect. Keeping Windows and your browser updated, and using antivirus software, significantly reduces this risk.