What to do if your computer has a virus
If your computer is infected, the fastest way to remove it is to boot into Safe Mode, run a full antivirus scan, and let the program quarantine or delete the infected files. Most modern antivirus tools — whether built-in like Windows Defender or third-party like Malwarebytes — can detect and remove common viruses without you needing to manually find them. The key is running the scan from Safe Mode, where fewer programs load and the virus has less ability to protect itself.
If your antivirus scan finds nothing but your computer still behaves strangely, the problem may not be a virus. Slow performance, pop-ups, and crashes can come from bloated software, a failing hard drive, or too many browser extensions. Before you assume infection, check whether the odd behavior started after you installed something new, or whether it happens only in one browser.
Key Takeaways
- Restart your computer in Safe Mode with Networking, then run a full antivirus scan — this is the standard first step and solves most infections.
- Windows Defender (built into Windows 10 and 11) is free and effective for most viruses; Malwarebytes is a second opinion if Defender finds nothing.
- If a scan finds infected files, let the antivirus quarantine them rather than manually deleting them, since deletion can sometimes break your system.
- If your computer still misbehaves after a clean scan, the problem is likely not a virus — consider a hard drive test, browser cleanup, or a factory reset.
- Never pay for virus removal over the phone or through a pop-up; legitimate antivirus software is free or costs under $50 per year.
How to boot into Safe Mode and scan
Safe Mode loads only the essential Windows files and drivers, which prevents most viruses from running. On Windows 10 or 11, restart your computer, and as it boots, press F8 or Shift+F8 repeatedly until you see the boot menu. Select "Safe Mode with Networking" — the "with Networking" part lets you download updates if needed.
Once in Safe Mode, open Windows Defender (search for "Windows Security" in the Start menu) and go to "Virus & threat protection." Click "Scan options" and choose "Full scan," then click "Scan now." This scan can take 30 minutes to several hours depending on how many files you have. Let it finish completely — do not restart or interrupt it.
If Windows Defender finds infected files, it will offer to quarantine them. Quarantine is safer than deletion because it isolates the files without removing them from your system, so if something goes wrong, you can restore them. Accept the quarantine, then restart your computer normally and check whether the problem is gone.
When to use Malwarebytes as a second opinion
If Windows Defender scans clean but your computer still has symptoms — constant pop-ups, redirected searches, or unexplained slowness — run Malwarebytes. It specializes in detecting adware and potentially unwanted programs that Windows Defender sometimes misses. Download Malwarebytes from malwarebytes.com on a clean computer or phone if your infected one will not let you, then transfer it via USB drive.
Install Malwarebytes, boot into Safe Mode again, and run a full scan. Malwarebytes is more aggressive than Defender and may flag programs you actually want to keep, so read the scan results carefully before removing anything. If you are unsure about a flagged item, search its name online — legitimate software will have clear documentation.
What to do if the antivirus will not run
Some viruses block antivirus software from opening or updating. If Windows Defender or Malwarebytes will not start, try these steps in order: first, restart in Safe Mode again and try opening the antivirus from there. Second, download the antivirus on a different computer, copy it to a USB drive, and run it from the USB on your infected machine. Third, use a bootable antivirus tool like Kaspersky Rescue Disk, which runs before Windows even loads.
To create a Kaspersky Rescue Disk, go to kaspersky.com/downloads/rescue-disk on a clean computer, download the ISO file, and follow their instructions to burn it to a USB drive or DVD. Boot your infected computer from that USB or disc, and Kaspersky will scan your entire drive without Windows interference. This method works even when the virus has locked down your operating system.
Signs your computer may not actually have a virus
Before you assume infection, check whether your symptoms match what a virus actually does. Viruses typically steal data, use your computer to attack others, or display ads. They rarely make your computer slow on their own — slowness usually comes from a full hard drive, too many browser extensions, or aging hardware. If your computer is slow but an antivirus scan finds nothing, run a disk cleanup and check your startup programs instead.
Pop-ups that appear only in your web browser usually come from a malicious website or a browser extension, not a system-wide virus. Try opening a different browser — if the pop-ups stop, the problem is in your original browser. Uninstall recent extensions, clear your browser cache, and reset your homepage. If pop-ups appear in every browser, then a system scan is warranted.
When to consider a factory reset
If multiple antivirus scans find nothing but your computer is still unstable, or if a virus has disabled Safe Mode itself, a factory reset may be your only option. A factory reset erases everything on your computer and reinstalls Windows from scratch, which removes any virus hiding in system files. On Windows 10 or 11, go to Settings > System > Recovery and click "Reset this PC." Choose "Remove everything" to erase all files, or "Keep my files" to preserve your documents.
Before you reset, back up any files you want to keep to an external drive or cloud storage. The reset process takes 30 minutes to an hour and will ask you to sign in with your Microsoft account when it finishes. After the reset, install antivirus software immediately and avoid downloading files from untrusted sources.
How to avoid reinfection
Most people get reinfected because they return to the same habits that caused the first infection. Viruses typically arrive through email attachments, downloads from suspicious websites, or fake software updates. Do not open email attachments from people you do not know, even if the email looks official. Do not download software from anywhere except the official website or the Microsoft Store.
Keep Windows and your antivirus definitions updated — set Windows Update to automatic, and let your antivirus update itself daily. Use a password manager to create strong, unique passwords for each website, so if one site is compromised, attackers cannot use the same password elsewhere. Enable two-factor authentication on important accounts like email and banking.
Frequently Asked Questions
Is Windows Defender good enough, or do I need paid antivirus?
Windows Defender is effective for most common viruses and costs nothing. Paid antivirus like Norton or McAfee offers extra features like VPN or password management, but they are not necessary for basic protection. If you want a second opinion tool, Malwarebytes free version is sufficient — you do not need the paid version unless you want real-time scanning.
What if I see a pop-up saying my computer is infected?
Pop-ups claiming your computer is infected are almost always scams. Do not click anything in the pop-up, do not call any number shown, and do not download anything it offers. Close the pop-up by clicking the X button or pressing Alt+F4. If the pop-up keeps returning, it is likely a browser extension or malicious website — try a different browser or clear your cache.
Can I remove a virus by just deleting the infected file myself?
You can, but it is risky. If you delete the wrong file or a file the operating system depends on, your computer may stop working. Let your antivirus quarantine files instead — quarantine isolates them safely. If you must delete manually, search the file name online first to confirm it is actually malicious and not a legitimate system file.
How long does a full antivirus scan take?
A full scan typically takes 30 minutes to two hours on a modern computer with a standard hard drive, or 15 to 45 minutes on a newer solid-state drive. The time depends on how many files you have and how fast your drive is. Do not interrupt the scan — let it finish completely so it checks every file.
What if my antivirus says a file is infected but I know I need it?
Search the file name online to verify whether it is actually malicious or a false positive. Legitimate software occasionally gets flagged by mistake. If you are confident it is safe, you can restore it from quarantine through your antivirus settings. If you are unsure, leave it quarantined — it is safer to lose a file than to restore something dangerous.