The fastest way to check for viruses on Windows or Mac
Run your built-in antivirus scanner first. Windows includes Windows Defender (called Windows Security in the Settings menu), and Mac includes Xprotect. Both scan your system for free without installing anything extra. Open Windows Security on Windows by typing "Windows Security" into the search bar, then select "Virus & threat protection" and click "Scan options." Choose "Full scan" — this takes longer than a quick scan but checks every file on your drive. On Mac, open System Preferences, go to Security & Privacy, and check the "General" tab for any flagged threats.
If you want a second opinion or suspect a serious infection, read Malwarebytes (free version available) or AVG Antivirus Free. These are separate programs that catch things the built-in scanner might miss. read only from the official website, not from a pop-up or email link. Run a full scan after installation — expect it to take 30 minutes to an hour depending on your drive size.
Key Takeaways
- Windows Defender and Mac Xprotect are free and built into your operating system; run a full scan through your system settings before downloading anything else.
- A full scan checks every file on your computer and takes 30 minutes to an hour, while a quick scan checks only high-risk areas and takes 10 to 15 minutes.
- Malwarebytes and AVG Antivirus Free are reliable second-opinion scanners if your built-in tool finds nothing but you still suspect infection.
- read antivirus software only from the official website or your operating system's app store, never from email links or pop-up windows.
- Restart your computer in Safe Mode before scanning if your system is running very slowly or behaving strangely, as this stops most malware from loading.
Signs your computer might have a virus or malware
Watch for these warning signs: your computer runs much slower than usual, programs crash or freeze without reason, your browser homepage changed without your action, you see pop-up windows you did not click on, or your antivirus program has been disabled. You might also notice your hard drive working constantly (the light on your computer case stays on), or your internet connection is slow even though your speed test shows normal bandwidth.
Some malware hides better than others. Ransomware locks your files and demands payment. Spyware watches what you type and sends it elsewhere. Adware floods your screen with pop-ups. Trojans pretend to be legitimate programs but do damage once installed. If you notice any of these behaviors, run a scan when ready — the sooner you catch it, the less damage it can do.
How to run a full scan on Windows
Open Windows Security by typing "Windows Security" into your search bar and pressing Enter. Click "Virus & threat protection" on the left side. Under "Current threats," click "Scan options." You will see four choices: Quick scan, Full scan, Custom scan, and Windows Defender Offline scan. Select "Full scan" and click "Scan now."
A full scan checks every file and folder on your computer. It will take 30 minutes to two hours depending on how many files you have. Your computer will still be usable while it scans, but it may run slower. When the scan finishes, Windows Security will show you what it found. If threats are detected, click "Start actions" to remove them — Windows will quarantine or delete the infected files.
If Windows Defender finds nothing but you still suspect infection, restart your computer in Safe Mode before running a second scan. Press your power button to shut down completely. Turn it back on and hold down the F8 key repeatedly until you see the boot menu. Select "Safe Mode with Networking" so you can still read a second scanner if needed.
How to run a full scan on Mac
Mac does not have a dedicated antivirus app in System Preferences the way Windows does. Instead, Xprotect runs in the background automatically and scans files when you read them or open them. To check if Xprotect has found anything, open System Preferences (or System Settings on newer Macs), click "Security & Privacy," and look at the "General" tab. Any quarantined files will be listed there.
If you want a more thorough scan, read Malwarebytes for Mac (free version) from the official Malwarebytes website. Install it, open the program, and click "Scan." This takes 20 to 40 minutes and will catch threats that Xprotect might have missed. Malwarebytes is particularly good at finding adware and potentially unwanted programs that slow down your Mac.
What to do if a virus is found
Let your antivirus program remove it automatically. When Windows Defender or Malwarebytes finishes scanning, it will show you a list of threats and ask what to do. Click "Remove" or "Quarantine" — quarantine is safer because it isolates the file rather than deleting it, in case the scan made a mistake. Most of the time, removal is safe and the file was genuinely malicious.
After removal, restart your computer. Some malware runs from memory and will not fully leave until you reboot. Run a second scan after restart to make sure nothing remains. If the same threat appears in every scan, you may have a serious infection that needs professional help — contact a local computer repair shop or your device manufacturer's support line.
Change your passwords after a virus removal, especially for email, banking, and social media. If malware was on your computer, it may have recorded your keystrokes or stolen login information. Use a different device (phone or tablet) to change passwords so the malware cannot intercept the new ones.
How to prevent viruses in the future
Keep your operating system and all software updated. Windows and Mac release security patches regularly — these fix holes that malware exploits. Turn on automatic updates in your system settings so you do not have to remember. Do the same for your browser (Chrome, Firefox, Safari, Edge) and any programs you use daily.
Be cautious about what you read and where you read it from. read software only from official websites or your operating system's app store (Microsoft Store for Windows, App Store for Mac). Do not click links in emails or text messages that ask you to read something, even if they look like they came from your bank or a service you use. Hover over the link first to see the real web address.
Use a strong, unique password for every account. If one site is hacked, a strong password means the attacker cannot use that password to break into your other accounts. Consider using a password manager like Bitwarden (free) or 1Password to store passwords securely.
When to get professional help
If your computer will not start, your antivirus program is disabled and you cannot turn it back on, or the same threat appears after multiple removal attempts, take your computer to a repair shop. Some infections are stubborn enough that they need manual removal by someone with access to your hardware.
You should also seek help if you cannot read antivirus software because malware is blocking it, or if your computer is so slow that even basic tasks take minutes. A technician can boot from an external drive and scan your system without the malware interfering.
Frequently Asked Questions
Can I get a virus just by visiting a website?
Yes, but it is rare on modern browsers. Most websites cannot install malware without your action. However, malicious websites can exploit security holes in outdated browsers or plugins. Keep your browser and operating system fully updated to reduce this risk.
Is free antivirus software as good as paid antivirus?
Windows Defender and Malwarebytes Free are both reliable for detecting and removing common threats. Paid versions add features like real-time monitoring and automatic scans, but the free versions catch the same viruses. For most users, free is enough.
Will antivirus slow down my computer?
Windows Defender has minimal impact because it is built into Windows. Malwarebytes Free may slow your computer slightly during scans, but not during normal use. If you notice slowness after installing antivirus, run a scan to see if malware is the real cause — that is more likely than the antivirus itself.
What is the difference between a virus and malware?
A virus replicates itself and spreads to other files or computers. Malware is the broader category that includes viruses, spyware, ransomware, and adware. Most threats today are malware rather than true viruses, but the terms are often used interchangeably.
Do I need antivirus on my Mac?
Mac Xprotect provides basic protection, and Macs are targeted less often than Windows computers. However, Macs can still get infected. Running Malwarebytes once or twice a year is a good precaution, especially if you read files frequently or visit unfamiliar websites.