How To Know If Your Computer Has Malware

Updated on October 6, 2026, by Xcitium

Malware is one of the most widespread types of cyber attacks used today and is increasing each year exponentially. It can appear in the form of software codes, scripts, active content, and other software that seems legitimate.

Malware comes in different variants. Some of the common forms of malware are worms, viruses, trojans, spyware, adware, and rootkits, etc., which can attack and damage, disable, or disrupt host computers and networks.

You may have malware if your computer suddenly becomes slow, crashes frequently, shows unexpected pop-ups or browser redirects, installs unknown programs, disables security software, or uses unusually high CPU or network resources. To confirm an infection, update your security software and run a full malware scan rather than relying on symptoms alone.

10 Signs Your Computer May Have Malware

Look for these common warning signs:

Your computer suddenly becomes slow.
Unexpected pop-ups or advertisements appear.
Your browser redirects to unfamiliar websites.
Programs or extensions appear that you did not install.
Your antivirus or firewall becomes disabled.
Your computer frequently freezes or crashes.
CPU, memory, disk, or network usage suddenly increases.
Files disappear, change, or become inaccessible.
Your accounts show unexpected activity.
Programs or system settings change without your permission.

One symptom alone does not confirm malware. A sudden combination of several unexplained changes is more concerning and should be investigated with a trusted security scan.

Here are some of the ways to tell if your computer has malware.

Disabled Antivirus

If your antivirus software is disabled, it may be a sign that your computer has been a victim of a malware attack.

Go to your computer settings and look at your antivirus software. If things are normal, your antivirus is enabled and doing what it supposed to do. The main red flag that you should look for whether your antivirus is disabled or not.

Disabling antivirus is the first thing hackers will do once they actually get into our computer as it will allow them easier access to navigate around your computer.

Fake virus Messages

One way that hackers may try to trick you is by sending you fake virus messages such as “YOUR COMPUTER MAY BE INFECTED.” Some of these even have verbal prompts. If your antivirus is working properly, it should keep malware from getting into your computer.

Fake virus messages are the most common method by which people get malware on their computers. When people click on the fake virus message, it will grant the hacker access to their computer.

Frequent Popups On your Computer Screen

If your computer screen is filled with frequent popups, it may be an indication of a malware infection. As mentioned earlier, the first thing hackers will do when getting into a computer is disabling their antivirus software and popup blocking software.

Unapproved Software Installed On Your Computer

In most computers, any software will not download automatically unless you approve or schedule it. If software begins downloading without warning or asking for approval, you need to stop it immediately as it may be a malware. Sometimes your computer may download a regular software update, but if your computer starts downloading some random software from random sources without your permission, then it is a clear sign of malware infection.

Preventing Malware

If you experience some or all of the above-mentioned signs, your computer is definitely infected with malware. Make sure to install an Antivirus software like the Xcitium Antivirus to get rid of the malware and prevent future attacks.

In a corporate setting, it is not as easy to thwart malware attacks with antivirus software. It requires advanced security solutions to protect all the endpoints across different locations. Xcitium Advanced Endpoint Protection is such a solution which has stopped over 85 Million Endpoints from being infected.

With Xcitium Advanced Endpoint Protection, you can get rid of existing as well as future malware. Xcitium AEP has successfully contained 32 Million unknown files of which 3.5 Million pieces are malware programs. Xcitium AEP had successfully stopped those malware programs from doing any harm.

Today is every day with Xcitium Advanced Endpoint Protection. It is the only solution that protects you from unknown files. No Xcitium AEP customer was infected with malware till now. Or by ransomware, EVER!

Try Xcitium Advanced Endpoint Protection. Call us at +1 888-256-2608 or email us at EnterpriseSolutions@comodo.com

How Can You Tell If Your Computer Has Malware?

Malware can affect system performance, browsers, security tools, files, accounts, and network activity.

Sign of Malware	What You Might Notice	How Concerning Is It?
Slow computer	Programs suddenly take longer to open	Medium
Pop-ups	Ads or fake security warnings appear unexpectedly	High
Browser redirects	Searches open unfamiliar websites	High
Unknown programs	New applications appear without permission	High
Disabled antivirus	Security software turns off unexpectedly	High
Frequent crashes	Computer freezes or restarts	Medium
High CPU usage	Fans run heavily while computer is idle	Medium
File changes	Files disappear or have unexpected changes	High
Account activity	Unknown logins or messages appear	High
Network activity	Unexpected traffic occurs while idle	Medium
Ransom message	Files are locked and payment is demanded	Critical

The strongest indicators are usually changes you did not authorize, especially when multiple warning signs appear together.

1. Your Computer Suddenly Becomes Slow

A sudden performance decrease can be a malware warning sign.

Malware may consume:

CPU
Memory
Disk resources
Network bandwidth

You may notice:

Applications taking longer to open
Slow startup
Frequent freezing
Loud fans
High CPU usage
Poor battery life

However, a slow computer does not automatically mean malware.

Low storage, background updates, old hardware, too many startup applications, and legitimate resource-intensive programs can cause similar symptoms.

The key word is suddenly.

If a normally responsive computer becomes unusually slow without an obvious explanation, investigate further.

2. You See Unexpected Pop-Ups

Frequent pop-ups can indicate:

Adware
Potentially unwanted applications
Malicious browser extensions
Browser notification abuse
Suspicious websites

Be particularly cautious if a pop-up says:

“Your PC is infected!”
“5 viruses detected!”
“Call Microsoft support now.”
“Your antivirus has expired.”
“Click here to remove malware.”

A webpage generally cannot determine that your entire computer contains multiple infections simply by displaying a browser message.

Do not install security software from an unexpected warning.

Instead, close the page and open your trusted security software directly.

3. Your Browser Keeps Redirecting You

Browser redirects can be another warning sign.

You may notice:

Searches opening unfamiliar websites
Homepage changing unexpectedly
Default search engine changing
New tabs opening automatically
Unknown extensions appearing
Excessive advertisements

Check your browser’s:

Extensions
Homepage
Search engine
Notification permissions
Proxy settings

Remove changes you know you did not authorize and run a malware scan.

4. Unknown Programs Appear on Your Computer

Software you do not remember installing deserves investigation.

Malware and potentially unwanted applications can arrive through:

Software bundles
Fake updates
Email attachments
Malicious downloads
Cracked software
Deceptive advertisements

Review recently installed applications.

However, do not delete software simply because its name looks unfamiliar.

Operating systems, drivers, hardware utilities, and legitimate applications often install components with technical names.

Verify the publisher and purpose before removing anything.

5. Your Antivirus Is Disabled

Security software that turns off unexpectedly can be a serious warning sign.

Some malware attempts to interfere with:

Antivirus
Firewall
Security updates
Task Manager
System utilities

Check whether your security protection is active.

If it has been disabled and you cannot turn it back on, treat the computer as potentially compromised and investigate immediately.

6. Your Computer Frequently Crashes or Freezes

Malware can interfere with system processes and cause:

Application crashes
Freezing
Unexpected restarts
System instability

But crashes are not proof of malware.

Other possible causes include:

Bad drivers
Hardware failure
Overheating
Software conflicts
Operating-system problems

If crashes appear alongside redirects, unknown applications, disabled security, or other suspicious behavior, malware becomes a stronger possibility.

7. CPU or Network Usage Is High When the Computer Is Idle

Open Task Manager on Windows and look at:

CPU
Memory
Disk
Network

Unexpected activity while the computer is idle may deserve investigation.

For example, malware could use resources to:

Communicate with remote infrastructure
Download additional files
Send stolen information
Perform unauthorized computation

However, legitimate applications also perform background activity.

Cloud synchronization, Windows Update, browsers, security software, and backup tools can all use system resources.

Treat unexplained resource usage as a clue rather than proof.

8. Files Have Changed or Disappeared

Some malware can:

Delete files
Modify files
Hide files
Encrypt files
Rename files

Pay particular attention if many files suddenly:

Have unfamiliar extensions
Cannot be opened
Have changed names
Become inaccessible

If files are suddenly encrypted and you receive a payment demand, the computer may be affected by ransomware.

Disconnect the affected computer from the network and avoid modifying encrypted evidence unnecessarily.

9. Your Accounts Show Activity You Don’t Recognize

Malware designed to steal credentials can target:

Email accounts
Social-media accounts
Banking credentials
Browser sessions
Saved passwords

Possible warning signs include:

Unknown login alerts
Password-reset messages you did not request
Messages sent from your account
Unrecognized sessions
Security settings changing

If you suspect credential theft, use a trusted, clean device to change important passwords and enable multi-factor authentication.

10. Your Computer Behaves Strangely

Malware can cause unexpected behavior such as:

Programs opening automatically
Settings changing
New desktop icons
Unknown startup applications
Browser extensions appearing
Security warnings disappearing
Applications closing unexpectedly

Unexpected changes are particularly important when they occur shortly after:

Opening an attachment
Installing unknown software
Downloading a cracked application
Clicking a suspicious link
Responding to a fake security alert

Does One Malware Symptom Mean My Computer Is Infected?

No. One symptom usually cannot confirm malware.

Many normal computer problems resemble malware symptoms.

Symptom	Malware Could Cause It	Other Possible Cause
Slow computer	Yes	Low RAM or old hardware
High CPU usage	Yes	Updates or legitimate software
Crashes	Yes	Driver or hardware problem
Pop-ups	Yes	Browser notifications
Slow internet	Yes	Network congestion
Low storage	Yes	Large legitimate files
Loud fan	Yes	Heavy application workload
Browser changes	Yes	Extension or user setting

Look for patterns of unexplained behavior, then confirm them with security tools.

How Do You Check If Your Computer Actually Has Malware?

The best way to move from suspicion to confirmation is to perform a security scan.

Step 1: Update Your Security Software

Install the latest security updates and threat-detection information.

Step 2: Run a Full Scan

A full scan checks a broader set of files and system locations than a quick scan.

Step 3: Review the Results

Check whether the scanner identifies:

Malware
Potentially unwanted applications
Suspicious files

Step 4: Quarantine Confirmed Threats

Follow the security product’s recommended remediation steps.

Step 5: Scan Again

Run another scan after remediation to determine whether threats remain.

Quick Scan vs. Full Scan vs. Offline Scan

Scan	What It Checks	When to Use It
Quick Scan	Common malware locations	Routine security checks
Full Scan	Broader files and system locations	When you suspect malware
Custom Scan	Selected files or folders	Checking a suspicious item
Offline Scan	System outside normal Windows operation	Persistent or hidden threats

If you think your computer may already be infected, use a full scan rather than relying only on a quick scan.

How to Check for Malware on Windows

Windows users can start with Windows Security or another trusted security product.

To scan with Windows Security:

Open Windows Security.
Select Virus & threat protection.
Open Scan options.
Select the appropriate scan.
Run the scan.
Review detected threats.
Quarantine or remove confirmed malware.
Restart if requested.
Scan again if suspicious behavior continues.

For persistent threats, consider Microsoft Defender Offline scan.

Can Malware Hide From Antivirus?

Yes.

Sophisticated malware may attempt to:

Obfuscate malicious code
Disable security software
Abuse legitimate tools
Run in memory
Inject code into legitimate processes
Change behavior to avoid detection

Organizations may therefore combine antivirus with:

Behavioral detection
Endpoint Detection and Response
Threat intelligence
Sandbox analysis
Network monitoring

What If My Malware Scan Says the Computer Is Clean?

A clean scan is reassuring, but it does not always explain suspicious behavior.

If problems continue:

Update the security software.
Run a full scan.
Consider an offline scan.
Review installed programs.
Check browser extensions.
Review startup applications.
Investigate unexplained network activity.
Check whether another legitimate system problem explains the symptoms.

For a business computer, contact your IT or security team if suspicious behavior persists.

Frequently Asked Questions

How do you know if your computer has malware?

Look for sudden slowdowns, pop-ups, redirects, unknown programs, disabled security software, file changes, and unusual system activity. Confirm suspicious symptoms with a full security scan.

What is the biggest sign of malware?

There is no single definitive symptom. Multiple unauthorized or unexplained changes are more concerning than one isolated problem.

Does a slow computer mean it has malware?

No. Malware can cause slowdowns, but hardware, storage, updates, and legitimate applications can too.

Can malware run without you knowing?

Yes. Some malware is designed to operate quietly in the background.

How can I check my computer for malware?

Update your security software and run a full system scan.

Can Task Manager show malware?

It can reveal suspicious activity, but Task Manager alone cannot confirm malware.

Are pop-ups a sign of malware?

They can be. Adware, malicious extensions, websites, and notification permissions can all generate pop-ups.

Can malware disable antivirus?

Some malware attempts to disable or interfere with security software.

What if antivirus finds nothing?

Update it, run a full or offline scan, and investigate persistent suspicious behavior.

What should I do if malware is found?

Quarantine confirmed threats, rescan the computer, update software, and protect potentially exposed accounts.

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