Signs Of Malware On PC

Updated on August 28, 2026, by Xcitium

What Are the Signs of Malware on a PC?

Common signs of malware on a PC include sudden slowdowns, frequent crashes, unexpected pop-ups, browser redirects, unknown programs, high CPU or disk usage, disabled security software, unusual network activity, missing or encrypted files, and suspicious account activity.

A single symptom does not automatically prove malware infection. Hardware problems, software bugs, browser settings, or background applications can cause similar issues. The safest response is to investigate with trusted security tools.

Several malware variants are specially designed for infecting PCs. Most PC users are not aware of these threats and believe that their PCs are safe from malware attacks.

If you have a PC, it is important to understand how malware infects your PC and the ways to prevent it.

15 Common Signs of Malware on Your PC

1. Your PC suddenly becomes slow.
2. Your computer freezes or crashes frequently.
3. Applications close or fail unexpectedly.
4. You see constant pop-ups or fake security warnings.
5. Your browser redirects to unfamiliar websites.
6. Your homepage or search engine changes without permission.
7. Unknown programs appear on the computer.
8. CPU, memory, disk, or network usage stays unusually high.
9. Antivirus or other security tools become disabled.
10. You cannot access security websites or system tools.
11. Files disappear, become corrupted, or are encrypted.
12. New browser extensions appear unexpectedly.
13. Emails or social posts are sent without your knowledge.
14. You see unusual login or account activity.
15. The PC behaves strangely even when you are not actively using it.

Microsoft currently lists slow performance, frequent crashes, and unexpected pop-ups or programs among common malware indicators. Norton also highlights disabled security tools, unauthorized email activity, and being locked out of the computer as stronger warning signs.

Signs Of Malware On Your Computer

One of the most widespread types of malware among PCs is adware. Adware is a type of malicious software which displays annoying pop-up advertising banners while a program is running. It presents ads through pop-up windows or bars that appear on the program’s UI (User Interface).

Some adware can secretly gather your personal information, track your browsing habits or even record your keystrokes. Similar to spyware, most adware programs are packaged with free software to lure users into downloading them.

Another type of malware that is widespread among PC users is the Trojan horse. It is a small piece of malicious code or program that looks legitimate. Users are typically tricked into downloading and executing it on their computer systems. A trojan can not only steal your sensitive data, but they can also give cybercriminals access to your computer, financial and personal information.

Malware can appear in the form of software codes, scripts, active content, and other software that seems legitimate. Most malware variants rely on security failures such as an outdated operating system and absence of antivirus programs to start the attack.

Here are a few telltale signs that your PC might be infected:

1. Your PC becomes slow and unresponsive
2. Your PC crashes and restarts frequently
3. Applications on your PC crash frequently
4. Your PC’s storage is inaccessible or corrupted
5. You see unusual error messages on your PC
6. You see unwanted popup messages

If you notice any of those signs, there is a high chance of malware infection on your PC.

How to Check a Windows PC for Malware

For Windows users:

1. Open Windows Security.
2. Go to Virus & threat protection.
3. Check that protection is enabled and current.
4. Open the scan options.
5. Run a Full scan when infection is suspected.
6. Review detected threats.
7. Quarantine or remove confirmed malware.
8. Restart when required.
9. Run another scan if necessary.

If suspicious activity continues, Microsoft guidance also recommends considering Microsoft Defender Offline for deeper checking.z

What Should You Do If You Suspect Malware?

Take these actions:

1. Avoid entering sensitive credentials if credential theft is possible.
2. Disconnect unnecessary network access if active compromise or spread is suspected.
3. Run an updated full malware scan.
4. Quarantine detected threats.
5. Restart if required.
6. Run another verification scan.
7. Update Windows and applications.
8. Change compromised passwords from a trusted device.
9. Enable MFA.
10. Review important accounts for suspicious activity.

For a business-owned device, contact the IT or security team before manually deleting files or rebuilding the system.

Malware Symptoms by Threat Type

Symptoms overlap, so the behavior alone may not reveal the exact malware family.

How Does Malware Get Onto a PC?

Common infection methods include:

• Phishing emails
• Malicious attachments
• Malicious links
• Fake software
• Pirated applications
• Infected USB drives
• Compromised websites
• Exploited vulnerabilities
• Malicious browser extensions

Microsoft similarly lists phishing, infected files, vulnerabilities, infected USB drives, and malicious websites among common malware entry paths.

How to Protect Your PC Against Malware

Malware can run in the background, and you cannot find it unless you have the best antivirus or virus removal software. This is also applicable to an organization with multiple endpoints operating at various locations.

The best way to protect your PC from malware is to install antivirus software and keep your PC’s operating system up-to-date by downloading regular security patches and updates.

When it comes to an organization’s security, antivirus products are not a viable option. The ideal way to disarm even the most potent malware is to have an advanced endpoint protection system. Xcitium Advanced Endpoint protection (AEP) is such a solution which provides real-time protection for all of your endpoints.

Xcitium AEP beats all other endpoint protection systems, because  it isolates malware from penetrating the company’s local area network at the device layer and executes them in the isolated or restricted system environment. It is the most intelligent endpoint protection solution that offers multiple layers of protection against known and unknown threats.

Get Xcitium Advanced Endpoint Protection today and secure your endpoints against any malware threats.

How to Prevent Malware on a PC

Use layered protection:

• Keep Windows updated.
• Update applications.
• Use reputable endpoint protection.
• Keep real-time protection enabled.
• Use MFA.
• Avoid suspicious attachments.
• Verify links before opening them.
• Download software from trusted sources.
• Avoid pirated software.
• Limit administrator privileges.
• Back up important files.
• Review browser extensions.
• Monitor suspicious behavior.

For businesses, Microsoft additionally recommends EDR, MDR, XDR, threat hunting, offline backups, and Zero Trust practices for stronger malware prevention and detection.

Frequently Asked Questions About Signs of Malware on a PC

What are the most common signs of malware on a PC?

Common signs include slow performance, frequent crashes, unexpected pop-ups, browser redirects, unknown programs, security software being disabled, high resource usage, inaccessible files, and suspicious account activity. (microsoft.com)

Does a slow PC mean I have malware?

Not necessarily. Malware can slow a PC, but low storage, insufficient memory, background applications, updates, or hardware problems can cause the same symptom.

Are pop-ups always a sign of malware?

No. Pop-ups can come from adware, but they can also be caused by misleading websites or browser notification permissions. Fake virus alerts are often scams rather than proof that the PC is infected. (learn.microsoft.com)

Why does malware disable antivirus software?

Some malware attempts to disable security products so it can remain active, download additional threats, or avoid detection.

Can malware make my browser redirect?

Yes. Adware, browser hijackers, malicious extensions, and other unwanted software can cause browser redirects or modify browser settings.

Can malware cause high CPU usage?

Yes. Malware such as cryptominers may consume significant processing resources, but high CPU usage can also come from legitimate software.

Can malware steal my passwords?

Yes. Credential-stealing malware, spyware, Trojans, and keyloggers may collect passwords or authentication data.

What should I do if I think my PC has malware?

Run an updated full security scan, quarantine confirmed threats, patch the operating system and applications, and change potentially exposed credentials from a trusted device. Use deeper or offline scanning if suspicious behavior continues.

Can malware hide from antivirus?

Some sophisticated threats may attempt to evade security software through obfuscation, rootkit techniques, fileless execution, or other methods. Businesses often supplement antivirus with EDR/XDR and continuous monitoring.

How do I know if the malware is gone?

After remediation, run another full scan and monitor the PC for recurring symptoms. Verify that security tools are working, browser behavior is normal, and suspicious account activity has stopped.

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