How to Scan Your Computer for Viruses: A Complete Step-by-Step Guide

To scan your computer for viruses, install legitimate antivirus software (Windows Defender is built into Windows), run a full system scan, and let it quarantine any threats it finds. Most scans take 15 minutes to 2 hours depending on your computer’s storage size. You don’t need to pay for premium antivirus if you’re starting out. Get the scan running today, then follow the removal steps below.

Why You Should Scan Your Computer Regularly

Viruses and malware hide themselves. They don’t announce their presence. You might have one running right now without knowing it. A virus quietly steals your passwords, slows down your computer, or uses your internet connection for attacks. Some steal banking information. Others lock your files and demand money.

The best defense is prevention, but scanning regularly catches infections before they cause major damage. Think of it like checking your doors and windows for break-ins. You’re taking inventory of what’s happening inside your system.

Most people wait until their computer feels slow or strange to scan. That’s reactive. Better approach? Scan every month whether something feels wrong or not. It takes less time than you think.

Signs Your Computer Might Be Infected

Before you scan, here are the real warning signs:

Your computer runs slower than normal. Programs open slower or freeze. Your browser acts strange: new tabs open automatically, or searches redirect to unfamiliar sites. Pop-ups appear constantly, even when you’re not browsing. Your antivirus software gets disabled or won’t open. Strange programs appear in your installed software list. Your internet slows to a crawl. The fan runs loudly for no reason. You see unexpected toolbars in your browser. Files or folders disappear or get renamed.

Any one of these means a scan is overdue. Multiple signs mean a scan is urgent.

The Three Types of Scans Explained

Different scans catch different problems. Understanding them helps you know what to run.

Quick Scan: This checks the most common locations where viruses hide. System files, startup folders, temporary files. Takes 5 to 10 minutes. Good for weekly quick checks. Won’t catch everything, but catches most active threats.

Full System Scan: This checks every file and folder on your computer, including external drives if connected. Takes 1 to 3 hours depending on how much data you have. This is thorough. If you suspect a serious infection, run this. First-time scan? Do a full scan.

Custom Scan: You pick specific folders or drives to scan. Use this when you downloaded something questionable or want to check just your Documents folder. Faster than full scan, but you pick the locations.

How to Scan Your Computer for Viruses on Windows

Step 1: Check Your Current Antivirus Status

Windows 10 and Windows 11 come with Windows Defender built in. It runs automatically in the background. You don’t need to install anything to get basic protection. This is your starting point.

Click the Windows icon in your taskbar. Type “Windows Security” and press Enter. The app opens. You should see “Virus and threat protection” on the left side. Click it. Look at the status. It should say “Your device is being protected.” Green checkmarks are good. Red X marks mean something needs fixing.

Don’t have Windows? That’s fine. Jump to the section below about third-party antivirus software.

Step 2: Run a Full Scan with Windows Defender

Open Windows Security again. Click “Virus and threat protection.” Look for “Manage settings” or “Scan options.” Some versions show “Run a new advanced scan.”

Click “Scan options.” You’ll see choices:

Quick scan is the default. Don’t use that for your first check.

Full scan is what you want. Select this option. Click the “Scan now” button.

Your computer starts scanning. A window shows progress. It displays how many files have been scanned and if any threats were found. Don’t worry if the scan takes time. This is normal. Your computer is working hard.

If threats are found, Windows Defender automatically quarantines them (isolates them so they can’t run). The scan result shows what was found. You can remove it or restore it. Select “Remove” unless you’re sure the file was harmless.

Step 3: Review and Remove Threats

After the scan finishes, a summary appears. It shows how many items were scanned. More importantly, it shows if anything was found.

Found items appear with names like “Trojan:Win32/Wacatac” or “PUA:Win32/Preflighter.” Don’t try to understand the technical names. Antivirus software handles the details. Just know that if antivirus flagged it, it’s suspicious.

Items in quarantine are neutralized. They can’t infect your system from quarantine. You can safely leave them there or delete them permanently. Most people delete them. Deleting is usually the right choice unless you know for certain it’s a false alarm (like a legitimate program Windows Defender misidentified).

Using Third-Party Antivirus Software

Windows Defender is solid for most people. But if you want a second opinion or need more features, third-party options exist.

Malwarebytes is popular. It’s good at finding specific malware that Windows Defender might miss. Free version does scans. Premium version adds real-time protection. Download from malwarebytes.com. Install it. Open it. Click “Scan” to start. Takes 20 to 45 minutes for a full scan.

Avast Free Security offers a complete free antivirus. Real-time protection included. Download from avast.com. Install and scan. Straightforward interface.

Norton 360 is paid but highly rated. Costs money but offers strong protection and extra features like password management.

Bitdefender is another paid option with excellent malware detection rates.

For most people, running Windows Defender plus Malwarebytes (free version) gives you solid coverage. Run Windows Defender monthly. If you suspect something, run Malwarebytes too. Two different tools catch different things.

How to Scan Your Mac for Viruses

Macs get viruses too. macOS includes Xprotect, built-in antivirus protection. It works in the background automatically.

You can’t manually open macOS’s built-in protection. But you can check activity.

Open System Preferences. Go to Security and Privacy. Check the General tab. You should see “Your Mac is protected.” That’s good.

For manual scanning on Mac, download Malwarebytes for Mac. It works similarly to the Windows version. Download, install, run scan.

Or use Avast Security for Mac. Free version available.

Macs are less targeted by viruses than Windows computers, but they’re not immune. Scanning every couple of months is still smart.

What to Do If Threats Are Found

Finding threats isn’t a disaster. It’s actually good news because you found them before they did serious damage.

After antivirus software quarantines threats, most of the danger is gone. The files are isolated and can’t run. Your next step depends on severity.

If a few suspicious files were found: Antivirus software already handled it. Allow it to remove them. Restart your computer. Scan again a few days later to make sure nothing else surfaced. You’re probably fine.

If many threats were found: This suggests active infection. After removal, change your passwords. Especially banking passwords, email passwords, social media. Do this from a different device if possible (like your phone). The infection might have stolen passwords.

If your computer still acts infected after scanning: Run another scan using a different tool. Windows Defender found something but maybe didn’t catch everything. Malwarebytes is good second choice.

If nothing worked: Your computer might have a serious infection or hardware problem. Consider taking it to a professional technician. They have advanced tools and experience.

Prevention: The Best Medicine

Scanning finds problems. Prevention stops them from starting.

Keep Windows updated. Go to Settings > Update and Security > Windows Update. Click “Check for updates.” Install everything. Updates patch security holes. Most infections use known vulnerabilities.

Same goes for other software. Chrome, Firefox, Java, Adobe Reader, Microsoft Office. They all release security updates. Let them update automatically when possible.

Don’t click links in emails from people you don’t know. Especially links promising money, refunds, or urgency. Criminals use email to distribute viruses. When in doubt, don’t click.

Download software only from official websites or trusted stores. Don’t use sketchy file-sharing sites. Legitimate programs come from official sources. Pirates and thieves use torrent sites and key generator websites. Free versions hosted on unknown sites often contain hidden viruses.

Disable browser extensions you don’t recognize. Malicious extensions spy on browsing, inject ads, or steal passwords. Go to Settings in your browser. Find Extensions or Add-ons. Delete anything you didn’t intentionally install.

Use strong passwords. Different passwords for different sites. Especially email and banking. If one site gets breached, attackers can’t get into everything. Password managers like Bitwarden or 1Password make this easier.

Disable file sharing if you’re not using it. Some older viruses spread through shared folders. Unless you actively need to share files with others, turn this off. Settings > Network and Sharing > Advanced sharing settings.

Use a firewall. Windows includes one. It’s usually on by default. Check Settings > Update and Security > Windows Defender Firewall. Should show “On” for both public and private networks.

These practices reduce your risk dramatically. Combined with regular scanning, you have solid protection.

Why Antivirus Slows Down Your Computer

You might notice your computer feels slower after installing antivirus software. That’s because antivirus constantly watches everything. Every file you open. Every program you run. Every website you visit.

This background monitoring uses CPU power and memory. On older computers with limited resources, you might notice the slowdown.

This is normal. The protection is worth the small performance hit. But if slowness is severe, you have options.

You can schedule scans for nighttime when you’re not using the computer. You can exclude certain folders from scanning if you trust them (though be careful with this). You can disable certain scanning features you don’t need. Or you can upgrade your computer’s RAM or use an SSD drive for faster processing.

For most modern computers from the last 5 to 10 years, the slowdown is barely noticeable.

Common Mistakes to Avoid

Mistake 1: Ignoring scan results. You run a scan. It finds threats. You close the window. Don’t do this. Let antivirus remove threats.

Mistake 2: Scanning only when something feels wrong. By then infection might be serious. Scan regularly whether something seems wrong or not.

Mistake 3: Using cracked antivirus software. Ironically, illegally downloaded antivirus programs often contain viruses themselves. Always download from official sources.

Mistake 4: Disabling antivirus to speed up your computer. This leaves you completely vulnerable. Don’t do it.

Mistake 5: Trusting scan results from random websites. Some sketchy websites claim to scan your computer online. They’re scams. They don’t actually scan. They just scare you into buying fake antivirus. Use software installed on your computer, not random websites.

Mistake 6: Assuming one scan means you’re safe forever. Malware evolves. Run scans regularly. Monthly is reasonable.

Quick Scanning Checklist

1. Open Windows Security or your antivirus software
2. Select “Full System Scan” or “Full Scan”
3. Click “Scan Now”
4. Wait for scan to complete (grab coffee, this takes time)
5. Review results
6. Remove or quarantine any threats found
7. Restart computer
8. Scan again in one week to confirm nothing returned
9. Schedule monthly scans in your calendar

When to Seek Professional Help

Most virus infections you can handle yourself. Sometimes you can’t. Seek professional help if:

Your computer won’t start. The operating system fails to load. Your antivirus software refuses to open or gets disabled repeatedly. Scanning finds thousands of threats and nothing removes them. Your computer still acts infected after multiple scans and removals using different software. You don’t feel comfortable taking these steps yourself. Sensitive data is involved (business information, financial records). You’re not sure what you’re doing and worried about making things worse.

Professional technicians have tools and experience you don’t. They recover data, remove stubborn infections, and restore systems. It costs money but sometimes that’s the best option.

Antivirus Options

Software	Price	Scan Speed	Detection Rate	Real-Time Protection	Best For
Windows Defender	Free	Fast	Good	Yes	Most Windows users
Malwarebytes Free	Free	Moderate	Excellent	No	Additional scanning
Avast Free	Free	Moderate	Good	Yes	Budget-conscious users
Norton 360	Paid	Fast	Excellent	Yes	Maximum protection
Bitdefender	Paid	Fast	Excellent	Yes	Advanced users

FAQs

How often should I scan my computer?

Monthly scans are good baseline. If you download a lot from the internet or visit risky websites, scan every two weeks. If you’re cautious with browsing and downloading, monthly works. If you suspect infection, scan immediately.

Will antivirus slow my computer down permanently?

Antivirus adds slight continuous overhead. Scans themselves slow your computer while running, but finish after an hour or so. The permanent slowdown from just having antivirus installed is usually minimal on modern computers, under 5% performance loss. If slowdown is severe, your computer might have other problems.

Can I remove a virus myself after antivirus finds it?

No, let the antivirus remove it. Antivirus software knows exactly what to delete and how to remove it safely. If you try manually, you might delete something important or miss related files. Always let the antivirus handle removal.

Is Windows Defender enough or do I need paid antivirus?

Windows Defender is good enough for most people. Paid options offer slightly better detection rates and extra features like VPN or password managers, but that extra 5 to 10% improvement doesn’t matter for casual users. Free is fine. If you want maximum protection and don’t mind paying, paid options are incrementally better.

What happens if antivirus finds something during my scan but I can’t delete it?

Some files lock themselves because they’re running. Restart your computer in Safe Mode. Windows runs only essential programs in Safe Mode. Then run the scan again. Locked files will delete more easily. If problems persist, the infection is serious and you need professional help.

Conclusion: Take Action Today

A virus hiding on your computer is more likely than you think. Millions of people use infected systems without realizing it. Slow performance, lost files, stolen data. These happen quietly.

Scanning takes one hour. That’s it. An hour now prevents days of problems later. You don’t need to be technical. You don’t need expensive software. Open Windows Security. Click scan. Let it run.

Today is the best time to scan. Do it this week. Then add monthly scanning to your routine. Your future self will thank you when your computer stays fast, safe, and problem-free.

Protecting your computer is easier than recovering from serious infection. Scan now. Protect yourself. The steps are simple. The benefit is huge.