The fastest way to check for a virus
Run a full scan with Windows Defender (built into Windows) or your antivirus software, then check the results. Windows Defender scans your entire hard drive and reports what it finds—threats it removed, threats it quarantined, or a clean bill of health. The scan takes 30 minutes to several hours depending on how much is on your drive. If you see threats listed, Windows Defender removes most of them automatically; if it cannot, it tells you what to do next.
If you use a Mac, run a scan with your antivirus software the same way. macOS includes some built-in protections, but a dedicated antivirus scan is more thorough. If you use Linux, antivirus software is less common because the operating system is less targeted by viruses, but you can still run a scan if you have installed antivirus software.
Do not wait for obvious signs. A virus does not always make your computer slow or crash. Many viruses sit quietly in the background stealing data or using your computer to attack other machines. A regular scan is your most reliable check.
Key Takeaways
- Windows Defender is free and built into Windows; run a full scan to check your entire drive for threats.
- A virus does not always make your computer noticeably slow or crash, so regular scans catch threats Windows Defender does not catch in real time.
- If a scan finds threats, Windows Defender removes most automatically; if it cannot, follow the on-screen instructions or contact support.
- Keep your operating system and antivirus software updated so they recognize the newest threats.
How to run a full scan in Windows Defender
Open Windows Security by clicking the Windows icon in the bottom left, typing "Windows Security," and pressing Enter. Click "Virus & threat protection" on the left side. Under "Current threats," click "Scan options." Select "Full scan" and click "Scan now." Windows Defender will begin scanning every file on your drive.
While the scan runs, you can use your computer normally, though it will be slower. When the scan finishes, Windows Security shows you the results. If it found threats, it tells you whether they were removed, quarantined (isolated so they cannot run), or left in place. Read the results carefully—if a threat was not removed, Windows Security explains why and what to do.
Run a full scan at least once a month, or more often if you read files frequently or visit unfamiliar websites. If you prefer, you can set Windows Defender to scan automatically on a schedule you choose.
What to do if a scan finds threats
If Windows Defender removes the threat automatically, the scan results will say "No current threats." Your computer is clean. If a threat was quarantined, it is isolated and cannot harm your computer, but Windows Defender is holding it in case you need to recover it later (rarely necessary).
If Windows Defender could not remove a threat, it will tell you the threat name and ask what you want to do. Some threats require you to restart your computer and run the scan again in Safe Mode—a stripped-down version of Windows that loads only essential files. To restart in Safe Mode, hold Shift while clicking the restart button, then choose "Troubleshoot" > "Advanced options" > "Startup Settings" > "Restart." When your computer restarts, press 4 or F4 to enter Safe Mode, then run the scan again.
If the threat still will not go away, write down the threat name and search for removal instructions specific to that threat. If you cannot remove it yourself, contact a computer repair professional or your computer manufacturer's support line.
Signs that suggest your computer might have a virus
Your computer is unusually slow, even when you are not running many programs. Programs crash or freeze without reason. Your browser homepage or search engine changed without you changing it. Pop-up windows appear constantly, even when you are not browsing the web. Your computer restarts on its own or shuts down unexpectedly.
New programs or toolbars appear that you did not install. Your antivirus software is disabled and you cannot turn it back on. Files or folders disappear. Your internet connection is slow even though your internet speed is normally fast. Your computer makes unusual sounds from the hard drive or fan.
None of these signs guarantees a virus—they can also mean a hardware problem, a failing hard drive, or a software conflict. But they are all reasons to run a full scan. A scan is the only way to know for certain.
Keeping your computer protected between scans
Keep Windows and your antivirus software updated. Windows updates include security patches that close holes viruses use to get in. Check for updates by clicking the Windows icon, typing "Check for updates," and pressing Enter. Install updates as soon as they are available, and restart your computer when prompted.
Do not open email attachments from people you do not know. Do not read files from unfamiliar websites. Do not click links in emails or text messages unless you are certain they are real—scammers send fake emails that look like they come from your bank or a company you use. If you are unsure, go to the company's website directly instead of clicking the link.
Use a strong password for your computer login and for important accounts like email and banking. A strong password has at least 12 characters and mixes uppercase letters, lowercase letters, numbers, and symbols. Enable two-factor authentication on accounts that offer it—this means you have to enter a code from your phone or email even if someone has your password.
When to use antivirus software other than Windows Defender
Windows Defender is free and catches most common threats. You do not need to buy a separate antivirus program unless you want extra features like a firewall, parental controls, or password management. If you do buy antivirus software, uninstall Windows Defender first—running two antivirus programs at the same time slows your computer and can cause conflicts.
Popular antivirus programs include Bitdefender, Norton, McAfee, and Kaspersky. They all work similarly: you install them, run a full scan, and let them monitor your computer in the background. Most charge a yearly fee. Before you buy, read reviews and check whether the program works well with your operating system and the other software you use.
If you cannot afford paid antivirus software, Windows Defender is sufficient for most people. The most important thing is to scan regularly and keep your operating system updated.
Frequently Asked Questions
How long does a full scan take?
A full scan usually takes 30 minutes to two hours on a newer computer with a solid-state drive, or two to four hours on an older computer with a traditional hard drive. The time depends on how much data is on your drive and how fast your computer is. You can use your computer while the scan runs, but it will be slower.
Can a virus hide from antivirus software?
Some viruses are designed to hide from antivirus software, but a full scan catches most of them because it checks every file on your drive, not just files that are running. If a virus hides successfully, it usually shows up the next time you run a scan or after you update your antivirus software with the latest threat definitions.
What is the difference between a virus, malware, and spyware?
A virus is a program that copies itself and spreads to other computers. Malware is a broad term for any malicious software, including viruses, spyware, ransomware, and others. Spyware is software that watches what you do and steals information like passwords or browsing history. Antivirus software catches all of these, so the distinction does not matter much for checking your computer—a scan finds them all.
Do I need to scan my computer if I have never had a virus?
Yes. Many viruses run silently in the background without obvious signs. You might have a virus and not know it. Scan your computer at least once a month, or more often if you read files frequently or use public Wi-Fi.
What should I do if I think a website gave me a virus?
Close the website when ready and do not read anything from it. Run a full scan with Windows Defender or your antivirus software. If the scan finds threats, follow the on-screen instructions to remove them. If you are worried you entered personal information on the website, change your passwords for important accounts like email and banking.