Fix Dual Antivirus Conflict: Disable Defender with 3rd Party
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If your antivirus — Norton is the biggest one that does this — is warning you that Windows Defender's "Periodic Scanning" is turned on, go to Windows Security > Virus & threat protection, click the link labeled Microsoft Defender Antivirus options sitting underneath your antivirus's own name, and switch the Periodic Scanning toggle at the bottom to Off. The counterintuitive part: this setting is off by default the moment a third-party antivirus is installed and working correctly. Most people who get this warning never turned it on themselves — and Windows doesn't log when or why a setting like this changes, so there's no way to say for certain what flipped it. What's certain is where the switch to undo it lives, and it isn't filed under Windows Defender at all. It's hidden behind a link with your own antivirus's name written on it.
Jake got asked about this by a customer who runs a small accounting office down the road — three PCs, all with a Norton subscription he'd bought after a phishing scare two years ago. One morning Norton popped up a security alert on all three machines at once, warning that "Periodic Scanning" was enabled in Windows Defender and recommending it be turned off. The customer's first reaction, reasonably, was that something had gone wrong: had Defender re-enabled itself? Was Norton failing? Neither. The setting had simply ended up on, with nothing in Windows telling her when or why.
That's the setting this guide is about: a genuinely useful, genuinely limited scanning mode that Microsoft Defender Antivirus can run in addition to your main antivirus, buried behind a menu link most people never open because it's named after their antivirus product, not after Defender.
What Periodic Scanning Actually Is
When Windows detects a third-party antivirus that's installed, registered, and working correctly, Microsoft Defender Antivirus's own real-time protection switches off — that part is automatic, and it's not the setting causing the warning. What's optional, and off by default in that situation, is limited periodic scanning: an occasional, lightweight scan Defender can run on top of your main antivirus, as a second opinion. Microsoft is upfront that it's a limited subset of Defender's full detection capability, not a full second layer of protection, and doesn't recommend it for business or enterprise machines — it's aimed at home users who want a little extra reassurance.
Where the confusion comes from is the toggle's location. It doesn't live in a section labeled "Windows Defender" at all. Open Windows Security, go to Virus & threat protection, and underneath the name of whatever antivirus you've got installed, a small link appears reading Microsoft Defender Antivirus options. Click that, and the Periodic Scanning toggle is at the bottom of the panel that opens. It's genuinely easy to have used a PC for years and never once seen this link, because there's no reason to click something labeled with your antivirus's own name unless you're specifically looking for Defender settings hiding underneath it.
♂️ Jake's Reality Check
"My customer swears she never touched a single antivirus setting on any of her three PCs. How did this get turned on across all of them?"
There's no way to say for certain, and that's worth telling her honestly. Windows doesn't keep a record of when a setting like this last changed or what changed it. A feature update, an OS upgrade, or a reinstall are all plausible causes, but none of them leave a trace you can actually check. It's not evidence of tampering or malware either way — just a setting Windows carries forward loosely across changes, with nothing telling you it moved.
Ethan's read on it, when Jake asked whether this was something to actually worry about: "It's not a security problem either way. If it's on, at worst you've got a mostly harmless background scan running occasionally. If it's off, you're relying entirely on the antivirus you're paying for, which is exactly what that antivirus is designed to handle on its own. The only real issue is that people get an alarming pop-up about a setting they've never seen, with no idea where to go fix it."
Turn It Off in Windows 11
1) Click the search icon on the taskbar (or press Win) and type Windows Security, then open it.
2) Select Virus & threat protection from the left-hand list.
3) Under "Virus & threat protection settings," you'll see the name of your installed antivirus. Directly beneath it, click Microsoft Defender Antivirus options.
4) A panel expands underneath, showing standard Defender options laid out the same way they'd appear if Defender were your primary antivirus. Scroll to the bottom to find Periodic Scanning.
5) Switch it to Off. No restart is required — it takes effect immediately, and Norton or whichever antivirus flagged it should stop warning you within its next check.
Turn It Off in Windows 10
These steps are the same as Windows 11. Both operating systems share the identical Windows Security app, and Microsoft has kept this particular panel consistent across both.
1) Search the taskbar for Windows Security and open it.
2) Click Virus & threat protection.
3) Under your antivirus's name, click Microsoft Defender Antivirus options.
4) Scroll to the bottom of the panel that opens and switch Periodic Scanning to Off.
What changed since we first wrote this
- Then: On the Windows 10 Anniversary Update, this feature sat directly inside "Windows Defender Settings," and was switched on by default the moment a third-party antivirus took over — you scrolled down and saw the toggle already showing On.
- Now: The equivalent setting is off by default, moved into the Windows Security app, and hidden behind a link labeled with your antivirus's own name rather than Defender's.
- What that means for you: If you're seeing a warning about it today, it's very unlikely you switched it on deliberately — but there's no log to point to exactly what did. The fix is the same regardless of the cause.
What It Means If You Don't See the Link at All
The "Microsoft Defender Antivirus options" link only appears when Windows currently recognizes your third-party antivirus as installed, registered, and working. If you open Virus & threat protection and there's no such link — just Defender's own standard options, front and center — that's worth paying attention to for a different reason: it usually means Windows doesn't consider your antivirus active right now, which means Defender's own real-time protection may have quietly switched itself back on underneath it.
⚠️ What this actually means
This isn't a Periodic Scanning problem at that point — it's a sign your paid antivirus has expired, failed to register with Windows properly, or was uninstalled without Windows noticing. Check your antivirus's own status window first. If it says it's active but Windows Security disagrees, a reinstall of the antivirus (through its own official installer, not a shortcut or leftover icon) is usually what fixes the mismatch.
Should You Turn It On Instead?
Because it's off by default, plenty of readers land here for the opposite reason: they've heard about limited periodic scanning and want the extra layer, deliberately. It's a reasonable thing to want, with one honest caveat worth knowing first.
✅ Why this is worth turning on for most home users
No single antivirus engine catches everything. A limited, occasional scan from a second engine — timed by Windows to avoid interfering with your main antivirus's real-time protection — costs very little and occasionally catches something the first engine missed. For a home PC, that trade-off usually favors turning it on.
The caveat: Microsoft is explicit that this mode uses only a limited subset of Defender's full detection capability, and it isn't meant to replace a properly maintained primary antivirus. It's an extra check, not a second line of full-strength defense — and it isn't supported or recommended on business or enterprise machines at all, where a single, centrally managed antivirus solution is the right call instead.
Edge Cases Worth Knowing About
Windows Home vs Windows Pro
Nothing here differs between editions. The Windows Security app, this menu, and the toggle itself are identical on Home and Pro. The only Pro-specific difference is that Microsoft explicitly discourages enabling this on business machines, and an IT administrator on a managed Pro, Enterprise, or Education device may have locked security settings centrally regardless of edition.
Small offices and multi-PC setups
Jake's accounting-office customer had the same warning appear on all three machines at once, which is common when several PCs share the same update schedule and configuration history. Fixing it once per machine, the same way, is normal — there's no single switch that covers several PCs unless they're centrally managed through Group Policy or Intune.
Migrating from an older Windows 10 build
If you're moving from an older Windows 10 build where this setting genuinely was on by default (the Anniversary Update era this guide originally covered), migrating to a current build doesn't automatically reset it. It can carry over from your old configuration exactly as it was, which is one more reason people find it on today without remembering turning it on.
The Task You'll Need Right After This
Once you've changed the setting, it's worth confirming your primary antivirus is actually the one Windows currently trusts. Open Windows Security and look at the top of the Virus & threat protection page: if a third-party antivirus is active and recognized, Windows Security shows its name and status there directly. If it instead shows Defender's own status front and center, your other antivirus isn't currently registered as working — the same situation covered above, worth resolving before you assume you're covered either way.
| Situation | What it means | What to do |
|---|---|---|
| Antivirus warns Periodic Scanning is on | It was switched on at some point — no log records exactly when or how | Turn it off via Microsoft Defender Antivirus options |
| You want the extra scan deliberately | It's a reasonable, limited extra layer for a home PC | Turn it on the same way, but keep your main antivirus as the real defense |
| The link isn't there at all | Windows doesn't currently see your antivirus as active | Check your antivirus's own status, then reinstall it if needed |
| Business or managed PC | Microsoft doesn't recommend this feature for enterprise use | Leave it to your primary antivirus and IT policy, not this toggle |
Frequently Asked Questions
Why is Norton specifically the one warning me about this?
Norton actively checks for this setting and raises a security alert when it finds it on, recommending you turn it off. Other antivirus products may not flag it the same way, even though the underlying Windows setting works identically regardless of which antivirus you use.
Does turning this off disable Windows Defender completely?
No. Defender's real-time protection already switched itself off automatically when your third-party antivirus took over. This setting only controls the additional, limited periodic scan Defender can run on top of that. Windows Firewall and other Windows protections are unaffected either way.
I never touched this setting. How did it get turned on?
There's no reliable way to know for certain — Windows doesn't log changes to this particular toggle. It's very unlikely you switched it on by accident through normal use, since it's buried behind a link named after your antivirus, not something you'd stumble into. A Windows update, an OS upgrade, or an antivirus reinstall are the most plausible explanations, but none of them can be confirmed after the fact. Either way, the fix is the same.
Is it safe to leave two antivirus engines running at once?
Running two full-time, real-time antivirus engines together is generally a bad idea because they can conflict over the same files. This feature is specifically designed to avoid that: it runs occasional, limited scans rather than continuous real-time protection, timed not to overlap with your primary antivirus's active scanning.
Can I use limited periodic scanning on a business PC?
Microsoft specifically advises against it on enterprise and business machines. It's built as a consumer feature, with reduced detection, management, and reporting compared to running Defender as a primary antivirus, and enterprises are better served choosing one primary antivirus solution and using it exclusively.
I can't find "Microsoft Defender Antivirus options" anywhere on my PC. What's wrong?
That link only shows up when Windows currently recognizes a third-party antivirus as installed and working. If it's missing, check whether your antivirus subscription has expired or failed to register properly — see the failure-mode section above.
Will limited periodic scanning slow down my PC?
It's designed to run occasionally and at low priority, timed to avoid interfering with your main antivirus's real-time scanning. Most users, especially on modern hardware, won't notice it running at all.
Does this setting exist on Windows 10 machines that are past end of support?
Yes. Windows Defender continues receiving virus definition updates on Windows 10 even after the October 2025 end-of-support date, and this setting works exactly as described whether or not you've enrolled in Extended Security Updates.
Does limited periodic scanning replace needing a real antivirus?
No. Microsoft is explicit that it uses only a limited subset of Defender's detection capability and can't be relied on to catch most malware on its own. It's meant to sit alongside a properly maintained primary antivirus, not instead of one.
If I turn it on, will it show up as a separate icon or process?
You may see Defender's own process appear briefly in Task Manager during a scan, but it won't add a permanent tray icon or run continuously the way a full antivirus does — it activates only for the periodic scan itself and then goes quiet.
Will disabling this affect my antivirus subscription or warranty?
No. This is a Windows setting, entirely separate from your antivirus vendor's subscription, license, or any hardware warranty.
Can I schedule exactly when the periodic scan runs?
Not through this particular toggle — it runs on Windows's own idle-time logic once enabled. If timing control matters more than simply turning the feature on or off, that's a separate, more advanced setup through Task Scheduler.
- ProgramData & Program Files Location in Windows 11 and 10
Useful next if you're already digging through system settings while sorting out an antivirus conflict.
Revision note. Originally published October 30, 2016. Rewritten August 14, 2026 for Windows 11 and Windows 10. Back then, this feature sat directly inside Windows Defender Settings and was switched on by default the moment a third-party antivirus took over. Microsoft has since moved it into the Windows Security app, changed the default to off, and hidden it behind a link with your antivirus's own name on it — which is exactly why so many people find it on without remembering turning it on themselves. If a security alert sent you here feeling like something's wrong with your PC, it isn't; you just found one of Windows's better-hidden switches.