Every copy of Windows 10 and 11 already includes Microsoft Defender Antivirus. It runs in real time out of the box and gets its updates through Windows Update, so you don't need to buy anything to have baseline protection. The more useful question isn't "which free antivirus should I install?" but "am I actually using the one I already have?"
Make sure Defender is on
- Open the Start menu, type Windows Security, and open it.
- Select Virus & threat protection.
- Green check marks mean you're fine. Yellow or red warnings come with a button to fix them.
If you install another antivirus, Defender's real-time protection switches off automatically and the other product takes over. That's by design: running two real-time scanners at once tends to cause conflicts and slowdowns.
How to run a scan
Go to Windows Security > Virus & threat protection > Scan options, choose a scan, and click Scan now.
| Scan type | What it does | When to use it |
|---|---|---|
| Quick scan | Checks the places malware usually hides | Routine checks, or as a first step |
| Full scan | Checks every file and running program | You suspect an infection; expect it to take a while |
| Custom scan | Checks only the folders or drives you pick | A USB stick, your Downloads folder |
| Microsoft Defender Antivirus (offline scan) | Restarts the PC and scans before Windows loads | Stubborn malware that hides from normal scans |
The offline scan restarts your computer, so save your work first. Afterward, you'll find the results under Protection history.
To check a single file or folder, right-click it in File Explorer and choose Scan with Microsoft Defender. On Windows 11 you may need to click Show more options first.
Turn on ransomware protection
Ransomware encrypts your files and demands payment to unlock them. Defender has a feature called Controlled folder access that blocks untrusted apps from changing files in protected folders like Documents, Pictures and Desktop. It's off by default because it occasionally blocks legitimate apps.
- Go to Windows Security > Virus & threat protection.
- Scroll down and select Manage ransomware protection.
- Switch Controlled folder access on.
If a program you trust suddenly can't save files, click the Windows Security notification and allow that app. Pair this with OneDrive or another backup so you have clean copies no matter what.
Updates matter as much as antivirus
A lot of malware gets in through security holes that were patched months ago. Antivirus can't fully make up for an unpatched system.
- Check Settings > Windows Update > Check for updates regularly.
- Keep your browser up to date (most update themselves; restart them occasionally so updates apply).
- Update or uninstall programs you no longer use.
When a second opinion helps
If Defender finds nothing but your PC still acts strangely (pop-ups, a browser homepage you didn't set, unknown programs at startup), an on-demand scanner can give a second opinion. These don't run in the background, so they won't conflict with Defender.
- Microsoft Safety Scanner is a free, portable scanner from Microsoft. It expires 10 days after you download it, so grab a fresh copy each time you need it.
- Several other security vendors offer free on-demand scanners or removal tools as well.
Third-party free antivirus suites are also an option if you prefer their interface or features. Just keep to one real-time product, read the installer screens carefully (some bundle browser extensions or offers), and download only from the vendor's official site.
Spot fake virus warnings and tech support scams
A browser window saying "Your PC is infected! Call this number now" is a scam. Real antivirus software doesn't alert you through a web page, and Microsoft doesn't put phone numbers in error messages.
Scareware and fake tech support follow a pattern:
- A full-screen pop-up with alarms, flashing text, or a countdown timer
- A "scan" that finds dozens of threats within seconds
- A phone number, or a push to download a "cleaner" or pay for a fix
- A caller who claims to be from Microsoft, your bank or your internet provider and wants remote access to your computer
What to do:
- Don't call, click, or download anything.
- Close the tab. If it won't close, press Ctrl+Shift+Esc to open Task Manager and end the browser.
- When you reopen the browser, don't restore the previous session.
- If you already let someone connect remotely, disconnect from the internet, uninstall the remote access app they had you install, change your passwords from another device, and call your bank if you shared payment details.
FAQ
Is Microsoft Defender good enough?
For most home users, Defender plus regular Windows updates plus some caution with downloads and email attachments is a solid baseline. Adding another product is a choice, not a requirement.
Can I run two antivirus programs at the same time?
Not two real-time ones. They can conflict and slow your PC. One real-time antivirus plus an occasional on-demand scan is the safer combination.
What about "PC optimizer" programs that find hundreds of problems?
Tools that scan for free and then ask for payment to "fix" issues often exaggerate results to make a sale. If Windows Security shows no threats, you generally don't need them.
Do I need antivirus on a Mac or phone?
That's a different topic. On Android and iPhone, the biggest risks are scam messages and apps from outside the official stores, so caution with links matters more than any app.