How to Install Antivirus in Windows 10 (or Use the Built-In Defender)

You usually don’t need to install anything: Windows 10 comes with Microsoft Defender Antivirus, and it is turned on by default. To check it, open Start, type Windows Security, open the app and select Virus & threat protection. If you’d rather use a third-party antivirus, remove any old trial first, download the installer from the vendor’s official site, run it, and then confirm that Windows Security lists the new product as your active provider.

Applies to: Windows 10 version 22H2 (Home and Pro). Windows 10 reached end of support on October 14, 2025, so the last section explains why antivirus alone isn’t enough on these PCs anymore.

Before you start

• Know the names. Windows Security is the app you open. Microsoft Defender Antivirus is the scanner inside it (older guides call it “Windows Defender” or “Windows Defender Security Center”). There is also a separate Microsoft Defender app for Microsoft 365 Personal and Family subscribers; you don’t need it to get antivirus on Windows 10.
• There is no separate Defender installer. Defender is part of Windows 10 and can’t be downloaded on its own. Download Center pages titled “Windows Defender” are admin guides or update packages, not a program to install.
• Use an administrator account. Installing security software requires approving a User Account Control (UAC) prompt.
• Check for S mode. Open Settings > Update & Security > Activation. If it says Windows 10 Home in S mode or Windows 10 Pro in S mode, the PC runs only Microsoft Store apps, so a regular antivirus installer won’t start. Microsoft’s S mode FAQ says the only antivirus known to be compatible with S mode is the built-in one.
• Run one real-time antivirus at a time. Two products scanning every file at once can slow the PC, quarantine each other’s files and cause crashes.

Method 1: Check and turn on the built-in Microsoft Defender

Start here even if you plan to install something else. It tells you what’s already protecting the PC.

1. Select Start, type Windows Security, and open it. You can also go to Settings > Update & Security > Windows Security and select Open Windows Security.
2. Select Virus & threat protection (the shield icon). If Defender is active, you’ll see Current threats with a Quick scan button. If another product is active, its name appears here instead.
3. Under Virus & threat protection settings, select Manage settings and make sure Real-time protection and Cloud-delivered protection are On. Approve the UAC prompt if one appears.
4. Go back, scroll to Virus & threat protection updates (called Protection updates on some builds), and select Check for updates. The page shows the security intelligence version and when it was last updated.
5. Select Quick scan to test it. A healthy PC finishes with “No current threats.”

If real-time protection keeps switching itself back on after you turn it off, that’s normal behavior, not a fault. Our guide to turning Windows Defender on or off in Windows 10 covers the toggles in more detail, and Microsoft’s Windows Security overview lists every section of the app.

Method 2: Install a third-party antivirus

Pick this method if you want extras that a paid suite bundles, such as a VPN, password manager, identity monitoring or parental controls, or if you already pay for a subscription. It isn’t needed just to have antivirus.

1. Remove any other antivirus. Open Settings > Apps > Apps & features, select the old product (often a preinstalled trial), and select Uninstall. Restart afterward. Some products leave pieces behind and need the vendor’s own removal tool; our steps to uninstall McAfee on Windows 10 show how that works. You don’t need to uninstall Microsoft Defender; it steps aside on its own.
2. Check that the product still supports Windows 10. Look at the vendor’s system requirements page. Many still list Windows 10, but check before you pay.
3. Get the installer from the vendor directly. Type the vendor’s address into the browser yourself or use the link in your purchase email. Skip search ads, pop-ups and “download” buttons on other sites, which are a common way to spread malware.
4. Run the installer. Open your Downloads folder and double-click the setup file. If it fails to start, right-click it and choose Run as administrator. Select Yes on the UAC prompt.
5. Watch the setup screens. Read each page before selecting Next or Install, and clear any checkboxes for extra toolbars, browsers or “recommended” apps you didn’t ask for.
6. Activate it. Sign in to the vendor account or enter the activation code or license key from your purchase. Free editions may only ask for an email address, such as [email protected].
7. Let it update and scan. Most products download fresh definitions and offer a first scan. Let both finish, then restart if the installer asks.

Confirm it worked

Open Windows Security > Virus & threat protection. After a successful install, the page names the new product, shows it as on, and offers Open app. Microsoft Defender Antivirus turns its own real-time protection off automatically at this point. The product’s icon should also appear in the notification area at the right end of the taskbar (select the ^ arrow to see hidden icons).

Want Defender as a backup scanner? Under the third-party product’s name, select Microsoft Defender Antivirus options and turn on Periodic scanning. Defender then scans occasionally without competing in real time. Microsoft’s page on limited periodic scanning notes that this catches far less than a full real-time scanner, so treat it as a second opinion only.

Going back to Microsoft Defender

Uninstall the third-party product from Settings > Apps > Apps & features and restart. Defender also turns back on by default when the other product’s subscription expires or stops updating. Open Virus & threat protection afterward to confirm it shows Defender again.

Troubleshooting

“This app can’t run on your PC” or the installer won’t open

Check for S mode first (see Before you start). Switching out of S mode is free but one-way. Otherwise, make sure you downloaded the correct installer for Windows rather than Mac or Android, and download a fresh copy in case the first one was corrupted.

Setup stops with an error about another security product

Leftovers from an earlier antivirus are the usual cause. Run that vendor’s removal tool, restart, and try again. Also install pending updates from Settings > Update & Security > Windows Update and confirm you have a few gigabytes of free space.

Windows Security says “No active antivirus provider”

A third-party product has expired or was partly removed. Renew it, or remove it completely and restart so Defender takes over.

Settings are grayed out or say “managed by your organization”

Group Policy or management software on a work or school PC controls the antivirus. Contact that IT department rather than installing your own.

The PC is slow after installing

Make sure only one product shows as active in Windows Security, and schedule full scans for times you aren’t using the PC.

Windows 10 end of support and antivirus

Windows 10 no longer gets free security patches. Defender still receives security intelligence updates on Windows 10 (Microsoft’s manual update page lists Windows 10 among supported systems), but antivirus can’t fix holes in Windows itself. Microsoft’s end of support page says Extended Security Updates keep patches coming through October 12, 2027. To stay covered, enroll in Windows 10 Extended Security Updates or move to Windows 11.

Frequently asked questions

Is Microsoft Defender good enough for a home PC?

For most people, yes. It provides real-time and cloud protection, ransomware protection through Controlled folder access, and SmartScreen checks on downloads. Paid suites mainly add features outside antivirus.

How do I update Defender on a PC that can’t reach Windows Update?

Download the package that matches your system (32-bit, 64-bit or ARM) from Microsoft’s manual update page on another connected PC, copy it over with a USB drive, and double-click it to install the latest definitions.

Are free antivirus programs safe?

Free editions from established vendors can work well, though they often show upgrade prompts and skip extras. Programs you’ve never heard of that are pushed by ads or pop-ups are a common malware trick.

A website says my PC is infected. Should I install what it offers?

No. Real security warnings come from Windows Security or your installed antivirus, never from a web page asking you to call a number or download a “cleaner.” Close the tab (use Task Manager if it won’t close), then scan for malware in Windows 10 to be sure.

Which scan should I run after installing?

Use a full scan once to check everything on the drive. If something keeps coming back, run a Microsoft Defender Offline scan from Scan options. It restarts the PC and scans before Windows loads, which helps remove stubborn malware.

Next step: open Windows Security now and confirm that one antivirus, and only one, shows as active and up to date.