If you want to know how to run a virus scan on Windows 11, the good news is that you already have a capable security tool built into your PC. Microsoft Defender Antivirus can scan your computer for viruses, spyware, ransomware, potentially unwanted applications, and other threats without requiring a separate antivirus program.

But which scan should you choose? Should you run a quick scan, full scan, or offline scan? And what should you do if Windows 11 actually finds something suspicious?

Think of a virus scan like checking every room in your house for an unwanted visitor. A quick scan checks the places where problems commonly appear, while a full scan takes much longer and examines far more files.

In this guide, we’ll walk through how to run a virus scan on Windows 11, explain every major scanning option, show you what to do when malware is detected, and share practical tips for keeping your computer protected.

Table of Contents

What Is a Virus Scan in Windows 11?

A virus scan examines files, programs, processes, and other areas of your Windows 11 computer for known or suspicious threats.

Windows 11 includes Microsoft Defender Antivirus, which is integrated into Windows Security. It continuously monitors your PC when real-time protection is enabled, but you can also manually start a scan whenever you want.

A manual scan can be useful if:

Your computer suddenly becomes slow.
You downloaded a suspicious file.
You clicked an unfamiliar link.
A USB drive came from another computer.
Pop-ups or redirects suddenly appear.
You notice unfamiliar applications.
Your browser behaves strangely.
You simply want reassurance that your PC is clean.

Why Should You Run a Virus Scan on Windows 11?

Modern malware doesn’t always announce itself with an obvious warning.

Sometimes a threat causes crashes or strange pop-ups. Other times, it may operate quietly in the background.

Regular malware scans can help identify suspicious software before it causes additional problems.

Running a scan is especially worthwhile after downloading software from an unfamiliar website, opening an unexpected attachment, or connecting removable storage that you don’t completely trust.

Which Antivirus Does Windows 11 Use?

For users who don’t install another compatible antivirus solution, Windows 11 includes Microsoft Defender Antivirus as part of Windows Security.

Windows Security brings several protection features together, including:

Virus & threat protection
Firewall and network protection
App and browser protection
Device security
Account protection
Ransomware-related protections
Real-time threat monitoring

The exact options available can vary depending on your Windows configuration, updates, and whether another antivirus product is installed.

How Do I Run a Quick Virus Scan on Windows 11?

A Quick scan is usually the easiest place to start.

It focuses on common locations where malware may be found and generally takes considerably less time than a full system scan.

Step 1: Open Windows Security

You can open Windows Security several ways.

The simplest method is:

Press the Windows key.
Type Windows Security.
Select Windows Security from the search results.

You can also open it through:

Settings > Privacy & security > Windows Security > Virus & threat protection

Step 2: Open Virus & Threat Protection

Inside Windows Security, select Virus & threat protection.

You’ll see information about your current antivirus protection and recent security activity.

Look for the section related to current threats or scanning options.

Step 3: Start a Quick Scan

Select Quick scan.

Windows will begin checking your computer.

While the scan runs, you can generally continue using Windows, although demanding applications may perform more slowly while security software is working.

Step 4: Review the Results

When the scan finishes, Windows Security will tell you whether any threats were detected.

If nothing is found, you’ll see a message indicating that no current threats were detected.

If Windows identifies something suspicious, don’t immediately panic. Continue to the remediation steps later in this guide.

How Do I Run a Full Virus Scan on Windows 11?

A Full scan checks significantly more of your system than a Quick scan.

It’s useful when you want a deeper examination of your computer or have a specific reason to suspect malware.

Step 1: Open Virus & Threat Protection

Open:

Windows Security > Virus & threat protection

Step 2: Select Scan Options

Under the scanning section, choose Scan options.

Windows will display several scan types.

Step 3: Choose Full Scan

Select Full scan.

Then choose Scan now.

Windows Defender will begin examining a much larger portion of your system.

Step 4: Let the Scan Finish

A full scan can take substantially longer than a quick scan.

The time depends on factors such as:

Number of files
Storage capacity
Drive speed
System performance
Number of running processes
Type and amount of data stored on the computer

If you have a large hard drive containing hundreds of thousands of files, don’t be surprised if the process takes a while.

Should You Use Your PC During a Full Scan?

You can usually continue using your computer, but intensive activity may slow the scan and your system.

For the least interruption, start a full scan when you’re not doing resource-heavy work.

How Do I Scan a Specific File or Folder?

You don’t always need to scan the entire computer.

If you downloaded one suspicious file, Windows can scan that specific item.

Scan a File

Locate the file in File Explorer.
Right-click the file.
Choose the Windows Security or Microsoft Defender scanning option available on your system.
Follow the prompts.

This approach is useful when you want to check a downloaded installer, archive, document, or other individual file before opening it.

Scan a Folder

You can similarly scan a folder when you want to check a particular collection of files without performing a complete system scan.

This can save time when you already know where the potentially suspicious content is located.

What Is a Custom Scan in Windows 11?

A Custom scan lets you choose a specific location to examine.

For example, you might want to scan:

A particular folder
An external drive
A USB flash drive
A downloaded file collection
A secondary storage location

To use it:

Open Windows Security.
Select Virus & threat protection.
Select Scan options.
Choose Custom scan.
Select Scan now.
Choose the location you want Windows to examine.

Custom scans are especially convenient when you don’t need a complete system check.

How Do I Scan a USB Drive for Viruses?

USB drives can transfer malicious files between computers, so scanning removable storage is a sensible precaution.

After connecting the USB drive:

Open File Explorer.
Find the USB drive.
Right-click it.
Select the available Microsoft Defender or Windows Security scan option.
Wait for the scan to finish.
Follow Windows Security’s recommendations if a threat is detected.

Avoid opening suspicious files on the USB drive before scanning it.

What Is Microsoft Defender Offline Scan?

Sometimes malware can interfere with normal Windows operation.

That’s where Microsoft Defender Offline can be useful.

An offline scan restarts the computer and performs a security check outside the normal Windows environment. This can make it harder for certain persistent threats to hide or interfere with detection.

You can generally find it under:

Windows Security > Virus & threat protection > Scan options > Microsoft Defender Antivirus (offline scan)

When Should You Use an Offline Scan?

Consider it when:

A threat repeatedly returns.
Windows Security recommends an offline scan.
You suspect persistent malware.
Normal scans aren’t resolving a security problem.
You notice behavior suggesting that malicious software may be interfering with Windows.

Save your work before starting because the process involves restarting the computer.

What Is the Difference Between Quick, Full, Custom, and Offline Scans?

Choosing the right scan is easier when you understand the differences.

Scan Type	What It Does	Typical Use
Quick Scan	Checks common locations	Routine checks
Full Scan	Examines much more of the system	Deeper investigation
Custom Scan	Checks a selected location	Specific files, folders, or drives
Offline Scan	Scans outside the normal Windows environment	Persistent or difficult threats

There isn’t one scan that’s appropriate for every situation.

A quick scan is convenient for routine checking, while a full or offline scan can be more appropriate when you have stronger reasons for concern.

How Do I Know If Windows Defender Found a Virus?

After scanning, Windows Security provides information about detected threats.

If a threat is detected, you may see details such as:

Threat name
Severity
Affected location
Recommended action
Current status

The terminology can look intimidating, especially if you’re not familiar with cybersecurity.

Don’t delete random system files manually just because their names look unfamiliar. Instead, review the detection and use Windows Security’s recommended action.

What Should I Do If Windows 11 Detects Malware?

If Microsoft Defender detects a threat, Windows may recommend an action such as removing or quarantining it.

Quarantine

Quarantine isolates a suspicious file so it cannot operate normally.

This can be useful because the file is separated from the rest of your system without requiring you to manually hunt it down.

Remove

Removal attempts to eliminate the detected threat from your computer.

If Windows recommends removing a confirmed malicious item, follow the security application’s instructions.

Don’t Ignore Repeated Detections

If the same threat repeatedly appears after removal, you may be dealing with persistent malware or a compromised application.

In that situation, consider running a full scan and, where appropriate, Microsoft Defender Offline.

How Do I Update Windows Defender Before Running a Scan?

Security software is most useful when its threat intelligence is current.

Before performing a scan, you can check for security intelligence updates through Windows Security.

A typical path is:

Windows Security > Virus & threat protection > Protection updates

Look for the option to check for updates.

Keeping Windows and Microsoft Defender updated helps your PC respond to newer threats.

How Often Should You Run a Virus Scan?

There isn’t a universal schedule that every Windows 11 user needs to follow.

For many users, Microsoft’s real-time protection provides continuous background monitoring, while manual scans can be useful when circumstances warrant them.

You may want to perform a manual scan when:

You download unfamiliar software.
You receive a suspicious attachment.
You connect an unknown USB drive.
Your computer begins behaving unusually.
A browser suddenly shows strange behavior.
Windows Security recommends further investigation.

If you regularly download files from many different sources, additional manual checks may make sense.

How Can I Tell If My Computer Might Have Malware?

No single symptom proves that a computer contains a virus.

However, unusual behavior deserves attention.

Possible warning signs include:

Unexpected pop-ups
Browser redirects
Unknown programs
Unusual security warnings
Sudden changes to browser settings
Unexplained system slowdowns
Frequent crashes
Unexpected network activity
Files behaving differently than expected

Keep in mind that these symptoms can also result from ordinary software problems, outdated drivers, insufficient storage, or other non-malware causes.

That’s why scanning is more useful than simply assuming that unusual behavior means you’ve been infected.

Why Is My Windows 11 Computer Running Slowly After a Scan?

Security scans can temporarily consume CPU, memory, storage, and disk resources.

This is particularly noticeable during a full scan on older computers or systems with slower storage.

You may notice:

Slower application launches
Increased disk activity
Higher CPU usage
Temporary system lag

Usually, performance returns closer to normal after the scan completes.

If your computer remains unusually slow afterward, investigate other possible causes instead of assuming the scan caused permanent performance problems.

How Do I Keep Windows 11 Protected After the Scan?

Running a virus scan is only one part of computer security.

Think of it like checking the locks on your house. A security check is useful, but keeping the doors and windows secure afterward matters too.

Follow these habits:

Keep Windows Updated

Install Windows updates regularly.

Updates can include security fixes and improvements that protect against newly discovered vulnerabilities.

Keep Security Protection Enabled

Avoid disabling real-time protection unless you have a specific, informed reason.

Download Software Carefully

Use reputable sources when installing applications.

Be particularly cautious with:

Pirated software
Unknown installers
Suspicious browser extensions
Unverified cracks or activators
Unexpected email attachments

Use Strong Account Security

Protect your Microsoft account with a strong, unique password and available multifactor authentication.

Be Careful With Links

Don’t assume a link is safe simply because it arrives in an email or message from someone you recognize.

Compromised accounts can sometimes send malicious content automatically.

Should I Install Another Antivirus Program?

Windows 11 already includes built-in antivirus protection through Microsoft Defender.

Whether you need another security product depends on your particular needs and setup.

Installing multiple products that provide overlapping real-time antivirus protection can sometimes cause conflicts or unnecessary resource usage.

If you choose third-party antivirus software, understand which security features it provides and how it interacts with Windows Security.

How Do I Run a Virus Scan Without Installing Anything?

You don’t need to download another antivirus application just to perform a basic malware scan on Windows 11.

Microsoft Defender Antivirus is integrated into Windows Security.

That means you can:

Open Windows Security.
Select Virus & threat protection.
Choose a scan type.
Start the scan.
Review the results.
Follow recommended remediation steps if necessary.

For many everyday situations, this is the simplest starting point.

What Should I Do If a Virus Scan Finds Nothing but Problems Continue?

A clean scan doesn’t automatically prove that every possible computer problem has been identified.

If strange behavior continues, consider other explanations.

For example:

An unwanted browser extension could be responsible.
A legitimate application may be malfunctioning.
Windows could have corrupted system files.
A driver could be causing crashes.
Your storage drive could be experiencing problems.
Another security product could be creating conflicts.
The problem may be caused by a website rather than malware.

You can also try a full scan if you initially performed only a quick scan.

If Windows Security specifically recommends further investigation, follow its guidance.

Can a Virus Scan Remove Every Threat?

No security tool can guarantee detection of every possible threat.

Cybersecurity is constantly changing. New malware can appear, and attackers can use techniques designed to avoid detection.

That doesn’t make antivirus scanning pointless. Quite the opposite: current security software, updates, safe browsing habits, and cautious downloads work together to reduce risk.

Think of antivirus protection as a smoke detector. A smoke detector is extremely useful, but you still don’t deliberately leave the kitchen unattended with something burning.

Quick Troubleshooting Tips for Windows 11 Virus Scans

If a scan doesn’t behave as expected, try these basic steps.

Windows Security Won’t Open

Restart your computer and try again.

If the issue persists, check whether another antivirus application is installed and controlling security protection.

Scan Gets Stuck

Give the scan some time, particularly if you’re running a full scan.

Large drives can take a long time to examine.

Windows Reports a Threat but Won’t Remove It

Restart Windows and run another scan.

If the threat persists, consider using Microsoft Defender Offline if appropriate.

Another Antivirus Is Installed

Third-party antivirus software may change which security features Windows Security displays or controls.

Check which antivirus product is currently active before troubleshooting Microsoft Defender.

A Simple Windows 11 Virus-Scanning Checklist

Use this checklist whenever you want to perform a security check:

Open Windows Security.
Select Virus & threat protection.
Check your protection status.
Confirm security intelligence is current.
Start a Quick scan for a routine check.
Use Full scan for a deeper examination.
Use Custom scan for a specific file, folder, or drive.
Consider Offline scan for persistent threats.
Review detected threats carefully.
Quarantine or remove confirmed threats as recommended.
Restart the computer if Windows requests it.
Keep Windows and security intelligence updated.

Frequently Asked Questions

1. How do I run a virus scan on Windows 11?

Open Windows Security, select Virus & threat protection, and choose Quick scan. For deeper checking, open Scan options and select Full scan.

2. Does Windows 11 have a built-in virus scanner?

Yes. Windows 11 includes Microsoft Defender Antivirus through the Windows Security application.

3. How long does a Windows 11 virus scan take?

A quick scan can finish relatively quickly, while a full scan may take considerably longer depending on your storage, number of files, and system performance.

4. Should I run a full scan instead of a quick scan?

Not necessarily. A quick scan is convenient for routine checks, while a full scan is more appropriate when you want a deeper examination or have a reason to suspect a problem.

5. What should I do if Windows Defender finds a virus?

Review the detection in Windows Security and follow the recommended remediation action, such as quarantine or removal. If the threat persists, a deeper scan or Microsoft Defender Offline scan may be appropriate.

Conclusion

Knowing how to run a virus scan on Windows 11 gives you a simple way to check your computer without immediately installing additional security software.

For a routine check, open Windows Security > Virus & threat protection and start a Quick scan. If you need a more thorough examination, use Full scan. For a particular file, folder, or USB drive, Custom scan can save time. If a persistent threat is suspected, Microsoft Defender Offline provides another scanning option.

The most important thing is not to wait until your computer is obviously compromised before thinking about security. Keep Windows updated, maintain active antivirus protection, download software carefully, and pay attention to unusual behavior.

A few minutes spent checking your PC today can save you considerably more trouble later.

Summary: Key Takeaways

Windows 11 includes Microsoft Defender Antivirus through Windows Security.
A Quick scan is useful for routine malware checks.
A Full scan examines substantially more of your system.
Custom scans let you check specific files, folders, or drives.
Microsoft Defender Offline can help investigate persistent threats.
Scan suspicious downloads and removable drives before opening questionable files.
Keep Windows and security intelligence updated.
Follow Windows Security’s recommended actions when threats are detected.
A clean scan doesn’t necessarily explain every computer problem.
Good browsing and downloading habits are just as important as antivirus protection.