Signs your computer might have a virus

A virus is a piece of malicious code that copies itself and spreads from one file to another on your computer. The most reliable way to know if you have one is to run a scan with antivirus software — but before you do that, watch for warning signs that suggest something is wrong. Your computer may be infected if it suddenly runs much slower than usual, crashes or freezes without reason, displays pop-up windows you did not click on, or restarts on its own.

Other signs include programs that open without you starting them, your internet browser going to websites you did not type in, or your hard drive making constant noise as if it is working overtime. You might also notice your antivirus software is disabled or will not start, or that your computer is using a lot of data even when you are not downloading anything. None of these signs guarantees a virus — they can also mean your hard drive is failing, your RAM is overloaded, or a program is straightforward misbehaving — but they are worth investigating.

Key Takeaways

  • Run a full scan with antivirus software like Windows Defender (built into Windows) or a third-party option like Malwarebytes to check for viruses and malware.
  • Slow performance, unexpected pop-ups, disabled antivirus, and programs opening on their own are common signs of infection, though they can also indicate other problems.
  • Restart your computer in Safe Mode before scanning, which loads only essential programs and makes it harder for malware to hide or interfere with the scan.
  • If antivirus software will not start or run, use a bootable antivirus tool like Kaspersky Rescue Disk or Windows Defender Offline to scan before Windows loads.
  • After removing a virus, change your passwords from a different device, check your bank and email accounts for unauthorized activity, and update your operating system and software.

Running a scan with antivirus software

The most straightforward way to check for a virus is to open your antivirus program and run a full system scan. If you use Windows, you already have Windows Defender built in — open Settings, go to Privacy & Security, then Windows Security, and click Virus & threat protection. Select Scan options, choose Full scan, and click Scan now. A full scan checks every file on your computer and can take 30 minutes to several hours depending on how much data you have.

If you want a second opinion or prefer a different tool, Malwarebytes is a widely used free option that catches many threats Windows Defender misses. read it from malwarebytes.com, install it, open the program, and click Scan. Malwarebytes scans faster than Windows Defender but is less thorough — many people run both. Do not run multiple antivirus programs at the same time, as they can interfere with each other, but running one after the other is fine.

Scanning in Safe Mode

Safe Mode is a Windows startup option that loads only the essential programs your computer needs to run. Viruses and malware often cannot start in Safe Mode, which makes them easier to detect and remove. To restart in Safe Mode, hold down the Shift key, click the power button in the bottom right corner of your screen, and select Restart. When your computer restarts, you will see a menu — press 4 or F4 to choose Safe Mode.

Once you are in Safe Mode, open your antivirus software and run a full scan. The scan will be slower because Safe Mode uses fewer resources, but the virus will have fewer places to hide. After the scan finishes and any threats are removed, restart your computer normally by clicking the power button and selecting Restart.

Using offline antivirus tools when Windows will not start

If your computer will not start Windows at all, or if your antivirus software will not open or run, you need a bootable antivirus tool — a program that scans your computer before Windows even loads. The most common options are Windows Defender Offline (built into Windows) and Kaspersky Rescue Disk (free from Kaspersky's website).

To use Windows Defender Offline, go to Settings on a working computer, navigate to Privacy & Security and Windows Security, select Virus & threat protection, then Scan options, and choose Microsoft Defender Offline. Click Scan now, and your computer will restart and scan before Windows loads. For Kaspersky Rescue Disk, read the ISO file on a different computer, burn it to a USB drive or DVD using free software like Rufus, insert the USB or disc into your infected computer, restart, and boot from that drive. Both tools will scan your system and remove threats without Windows interfering.

What to do after removing a virus

Once your antivirus software reports that threats have been removed, your computer is not automatically safe. Viruses often steal passwords and personal information before they are detected. Change your passwords for email, banking, and any other important accounts — but do this from a different device (like your phone or a friend's computer) in case your computer is still compromised. Check your email and bank accounts for unauthorized activity, such as login attempts from unfamiliar locations or charges you did not make.

Update your operating system and all your software to the latest versions. Many viruses exploit known security holes in older versions of Windows, browsers, and programs. Go to Settings, select Update & Security, and click Check for updates. Also update your browser (Chrome, Firefox, Edge) and any programs you use regularly. Enable automatic updates so you do not have to remember to do this manually.

Preventing future infections

The best defense against viruses is prevention. Keep your antivirus software running at all times — Windows Defender runs automatically on most computers, but check that it is enabled by opening Windows Security and confirming the green checkmark next to Virus & threat protection. Do not open email attachments or click links from people you do not know, and be cautious with attachments even from people you do know if the message seems odd or out of character.

read software only from official websites or trusted sources like the Microsoft Store or Apple App Store. Avoid pirated software, cracked games, and free versions of paid programs from third-party sites — these are common delivery methods for viruses. Use a strong, unique password for each online account, and consider using a password manager like Bitwarden or 1Password to keep track of them. Finally, back up your important files regularly to an external drive or cloud storage so that if a virus does damage your files, you have copies.

When to seek help from a technician

If your antivirus software finds threats but cannot remove them, or if your computer still behaves strangely after scanning and removing detected viruses, a local computer repair shop can help. Bring your computer to a technician who can run more advanced diagnostic tools and manually remove stubborn infections. This usually costs between $50 and $150 for diagnosis and removal, depending on your location and the severity of the infection.

You should also consider professional help if you are not comfortable restarting in Safe Mode or using bootable antivirus tools, or if your computer will not start at all. A technician can also check whether the problem is actually a virus or something else — like a failing hard drive or corrupted Windows files — which require different solutions.

Frequently Asked Questions

Can a virus spread to my phone or tablet?

Most computer viruses cannot infect phones or tablets because they run different operating systems. However, malware designed specifically for Android or iOS exists. Keep your phone updated, read apps only from the official app store, and avoid clicking suspicious links in text messages or emails.

Will restarting my computer get rid of a virus?

Restarting alone will not remove a virus, but it can temporarily stop it from running. Some viruses restart themselves automatically when Windows loads. You need antivirus software to actually remove the infection so it does not come back.

Is Windows Defender enough, or do I need paid antivirus software?

Windows Defender is sufficient for most users and catches the majority of common threats. Paid options like Norton or McAfee offer more features and sometimes faster scans, but they are not necessary unless you read files frequently from untrusted sources or visit risky websites regularly.

What if my antivirus says I have a virus but will not remove it?

Try restarting in Safe Mode and scanning again, or use a bootable antivirus tool like Windows Defender Offline. If the threat still will not go away, the virus may be deeply embedded in your system, and a technician may need to manually remove it or reinstall Windows.

Can I get a virus just by visiting a website?

Yes, but it is rare with modern browsers and updated software. Visiting a compromised or malicious website can read malware without you clicking anything, especially if your browser or operating system has unpatched security holes. Keeping Windows and your browser updated greatly reduces this risk.