Start with the built-in scanner your operating system already has
Windows and Mac both include free malware scanners you can run right now without downloading anything extra. On Windows 10 or 11, open Windows Security (search for it in the Start menu), click "Virus & threat protection," then "Scan options." Choose "Full scan" and click "Scan now." This takes 30 minutes to several hours depending on how much is on your computer, but it checks every file. On Mac, open System Settings, go to General, then Security & Privacy, and look for any security alerts — macOS runs background scans automatically, but you can also run a manual check through Activity Monitor if you suspect a problem.
These built-in tools catch the majority of common viruses and malware because they use the same threat databases that paid antivirus companies use. They are not flashy, they do not send you alerts every five minutes, and they do not try to sell you upgrades — which is exactly why they work well. If the scan finds something, Windows Security will quarantine it (move it to a safe holding area) and offer to remove it. Do not hesitate to let it remove anything it flags.
Key Takeaways
- Windows Security and macOS's built-in protection catch most common viruses without you installing anything, and a full scan takes 30 minutes to a few hours.
- If your computer is running slowly, crashing, or showing pop-ups you did not click, run a scan immediately — these are the most common signs of infection.
- A second opinion from a free tool like Malwarebytes can catch things the first scan missed, especially if you think you have been infected for a while.
- After removing a virus, change your passwords from a different device, because malware often captures login information before it gets removed.
Recognize the signs that your computer might be infected
A virus or malware does not always announce itself. Watch for your computer running noticeably slower than usual, programs crashing without reason, your browser homepage changing on its own, or pop-up windows appearing even when you are not browsing. Some malware runs silently in the background stealing information, so you might not notice anything wrong until you see unauthorized charges on a credit card or a password that no longer works.
If you notice any of these signs, do not panic — but do run a scan before you do anything else online. Shut down other programs first so the scan can use your computer's full power. If you have been using the same passwords on multiple sites, plan to change them after the scan completes, because malware often captures login information before it gets removed.
Use a second scanner if the first one finds nothing but you still suspect infection
Sometimes malware hides from one scanner but not another, because different tools look for different signatures and behaviors. If Windows Security or macOS's built-in protection ran a full scan and found nothing, but your computer still feels wrong, download Malwarebytes (the free version). It is designed specifically to catch things that slip past general antivirus tools. Go to malwarebytes.com, download the installer, run it, and let it scan your entire system.
Malwarebytes is not a replacement for your built-in protection — it is a second opinion. Run it once, let it remove anything it finds, then restart your computer. If Malwarebytes also finds nothing and your computer is still behaving strangely, the problem might not be malware at all. A failing hard drive, a driver that needs updating, or even too many programs running at startup can cause the same symptoms.
Check what programs are running at startup
Malware often installs itself to run automatically every time you turn on your computer, which slows everything down. On Windows, press Ctrl+Shift+Esc to open Task Manager, click the "Startup" tab, and look at the list. Anything you do not recognize or do not remember installing should be disabled — right-click it and select "Disable." Common legitimate programs like Spotify, Adobe, and Microsoft Office often start automatically, so do not remove those unless you want to speed up startup time anyway.
On Mac, go to System Settings, click "General," then "Login Items," and look at what is listed under "Allow in the Login Window" and "Allow in the Menu Bar." Remove anything suspicious. Be cautious but not paranoid — if you do not recognize a program name, search for it online before disabling it. Disabling a startup program does not remove it; it just stops it from running automatically.
Keep your operating system and software updated
Most viruses and malware exploit known security holes in Windows, Mac, browsers, and other software. When Microsoft, Apple, or Mozilla release an update, they are usually patching a hole that hackers were already trying to use. On Windows, go to Settings, click "Update & Security," and select "Check for updates." On Mac, go to System Settings, click "General," then "Software Update." Let updates install as soon as they are available, and restart your computer when prompted — delaying updates leaves you exposed.
The same goes for your browser and plugins. Chrome, Firefox, Safari, and Edge all update automatically, but older versions of Adobe Flash, Java, and other plugins are common entry points for malware. If you have not used a plugin in years, uninstall it. If you use one regularly, check its settings to make sure automatic updates are turned on.
Understand what antivirus software actually does and does not do
Antivirus and antimalware tools work by comparing files on your computer against a database of known threats. If a file matches a known virus signature, the tool quarantines it. This works well for widespread malware that thousands of people have already encountered. It works poorly for brand-new malware that was created yesterday, because it is not in the database yet. No antivirus tool catches everything, and anyone who claims theirs does is selling something.
The best protection is not a tool — it is behavior. Do not download files from untrusted websites, do not open email attachments from people you do not know, do not click links in unsolicited messages, and do not give websites permission to run scripts unless you trust them. These habits stop most infections before they start. Antivirus tools are the safety net for the times you slip up.
What to do if a scan finds a virus
If Windows Security, Malwarebytes, or another scanner finds malware, let it remove the threat. The tool will usually quarantine the file (move it to a safe holding area where it cannot run) and offer to delete it permanently. Click yes. Restart your computer when prompted. After the restart, run the scan again to make sure nothing was missed — sometimes malware has multiple components.
After removal, change your passwords from a different device if possible. If you only have one computer, change passwords after the malware is removed and your computer has restarted. Start with passwords for email and banking, since those are the most valuable to a thief. If you see unauthorized charges on a credit card or account, contact your bank or credit card company immediately — they have fraud protection that can reverse charges and lock your account.
Frequently Asked Questions
How often should I scan my computer for viruses?
If you have built-in protection enabled and you keep your operating system updated, a monthly full scan is enough for most people. If you download files frequently from the internet or visit risky websites, scan weekly. If you notice your computer acting strangely, scan immediately.
Is it safe to download antivirus software from the internet?
Download only from the official website of the company that makes the software. For Malwarebytes, go to malwarebytes.com directly — do not click a link from an ad or search result. Fake antivirus programs are a common malware delivery method. If you are unsure, stick with your built-in Windows Security or macOS protection.
Can a virus survive if I restart my computer?
Most viruses survive a restart because they install themselves in files on your hard drive. Some malware runs only in your computer's memory and disappears when you shut down, but you cannot count on that. A restart alone will not remove an infection — you need to run a scanner and let it remove what it finds.
What if my computer will not start after I remove a virus?
This is rare but can happen if malware was deeply embedded in system files. Try restarting in Safe Mode (hold Shift while clicking restart on Windows, or hold Command+S while starting on Mac) and running a scan from there. If that does not work, you may need to take your computer to a repair shop or reinstall your operating system.
Do I need paid antivirus software if Windows Security is free?
Windows Security is sufficient for most people. Paid antivirus software sometimes catches additional threats, but it also uses more of your computer's resources and often tries to sell you extra features. If you download files constantly or visit many untrusted websites, paid software might be worth it — but your behavior matters more than your tool.