Do I need Malwarebytes and Microsoft Defender together?

No. Do not run Malwarebytes real-time protection and Microsoft Defender Antivirus at the same time. Microsoft’s support FAQ says you should not run other antivirus or antispyware products alongside Windows Defender, because two real-time scanners can slow the PC and cause install or update errors (including 0x80070643). CISA tells households to keep the operating system’s native antivirus on and updated. The question “is Defender enough?” is a different page: Is Microsoft Defender enough. This page is only about stacking. An on-demand Malwarebytes scan (the kind you start yourself, then close) is different from leaving two live shields on. Pick one real-time engine. Buying nothing extra is valid if Defender is already on.

The short answer

Do not run two real-time antivirus products at once; keep Defender, or switch to one other live engine, not both.

Microsoft’s FAQ is blunt: its security software already covers malware, spyware, adware, and other unwanted software, and you do not need another real-time antivirus or antispyware product. CISA’s household training says most operating systems already include a native antivirus, so you do not have to pick a third-party product just to have a scanner. CyberGuardLab is independent. We are not a Microsoft or Malwarebytes partner. We do not invent lab scores. “Use Defender and good habits” is a complete recommendation for many homes.

Why two real-time scanners fight

Two live antivirus engines can scan the same files at the same time and fight over updates; that is a performance and reliability problem, not extra safety.

Microsoft’s FAQ asks whether you should run Microsoft security software at the same time as other security products. The answer is no. Using more than one real-time security product can affect the PC’s performance. You might also get an error when you try to update or install, such as 0x80070643. If you install Microsoft’s software, Microsoft says to uninstall the previous security product.

CISA’s takeaway is the native stack plus updates, not a pile of brands: regularly update the OS and apps, use the native antivirus, and do not rely on antivirus alone while ignoring patches. CISA also warns that browser pop-ups dressed up as antivirus are often malware. A second free-scanner banner is not a reason to stack. See 8 ways to tell a virus warning popup is fake.

Windows Security is the built-in app. Microsoft describes it as a comprehensive solution that includes Microsoft Defender Antivirus, Windows Firewall, and related controls, on from the first boot. Real-time protection scans files you open or download. Turn that off with no other product installed and the PC is unprotected until it turns itself back on.

Real-time vs on-demand

A second on-demand scan is allowed; a second always-on shield is not.

Microsoft draws this line in the same FAQ. On-demand tools such as Microsoft Safety Scanner or Microsoft Defender Offline can sit next to any real-time product because they run when you ask, or on a schedule you set, and then stop. That is the useful distinction for Malwarebytes in a home:

Malwarebytes Premium (or any paid always-on mode) is the stacking risk. A free or trial build that only scans when you click Scan is closer to an on-demand tool. Check the Malwarebytes tray: if real-time protection, web protection, or exploit protection is on while Defender real-time is also on, you are in the do-not row. We are not reprinting Malwarebytes marketing names as scores.

How to pick one engine

Choose one live antivirus, confirm it in Windows Security, and treat a second brand as a one-time scan or a full replacement — not a roommate.

1. Open Windows Security. Start → Windows Security. Green checks on Virus & threat protection and Firewall & network protection are the baseline. Microsoft: search for the app in the Start menu.
2. See who is protecting you. Open Virus & threat protection. Under Who’s protecting me? or Manage providers, note the active real-time provider. If Microsoft Defender Antivirus is listed and real-time is on, you already have a live engine.
3. Turn Defender real-time on if nothing else is live. Virus & threat protection → Manage settings → Real-time protection On. Microsoft also calls Cloud-delivered protection and Automatic sample submission optimal when those toggles exist.
4. If Malwarebytes real-time is on, pick a lane. Lane A: keep Defender. Turn off Malwarebytes real-time modules (or uninstall Malwarebytes if you do not want the extra app). Lane B: keep Malwarebytes as the live engine and let Defender stand down. Microsoft says you can turn Defender off if you use a different security product, and that the device is vulnerable if you disable Defender with no other product.
5. Do not add a third leftover. New PCs often ship with a McAfee or Avast trial. Two leftovers plus Defender is worse. Use How to uninstall McAfee or Avast and use Windows Defender if that is the mess. This page is not that uninstall walkthrough.
6. Update Windows. Microsoft: Defender definition and engine updates arrive through Windows Update. CISA: keep the OS and apps patched; antivirus is the second line, not a substitute for updates.
7. Run one scan you understand. In Windows Security, run a Quick scan. Microsoft: a quick scan checks likely hiding places; a full scan looks everywhere and may slow the PC. If you still want a second opinion, run an on-demand scanner (Malwarebytes with real-time off, or Microsoft Safety Scanner), then close it.
8. If the PC is already a mess, clean it — do not stack. Use 9 steps to clean a virus-infected Windows PC. Panic-installing a second live AV on a sick machine is how update errors start.

If you already installed both

Leave one real-time product; uninstall or disable the other live shield rather than just turning both to max.

Check the Malwarebytes settings for real-time / web / exploit protection and switch those off if Defender is staying. Check Windows Security again. If Malwarebytes is now the listed provider, that is fine — you chose lane B. If both still claim real-time, reboot once and look again; leftover drivers sometimes keep a second scanner alive until you uninstall.

Microsoft’s FAQ: if you do not have another security product, or it is expired, Microsoft Defender Antivirus will automatically turn on. That is the usual ending after a trial dies. You can also enable Defender manually.

On-demand leftovers are less urgent. An icon that only runs when you click it is not the same as two shields. Still delete it if the household keeps launching it to be safe every hour and wondering why the fan is loud.

This is not “is Defender enough”

Enough-vs-paid-extras is the other guide; this guide is only about running two live scanners.

Is Microsoft Defender enough answers whether a typical updated Windows 10 or 11 PC needs to buy antivirus at all. This page assumes you already have Defender (or just installed Malwarebytes) and asks whether to stack. The answers can both be “buy nothing.” A paid suite is for extras you can name — VPN, password manager, identity monitoring, more phones — listed in 5 antivirus extras worth paying for in 2026. Stacking two real-time AVs is not an extra. It is the thing Microsoft tells you not to do.

What this page is not

This is not a Malwarebytes review, not a ranked best-antivirus-2026 chart, and not an exploit or bypass write-up.

It does not claim Defender never misses malware. CISA says no single antivirus guarantees 100% protection. The claim is narrower: two live engines are not the fix. It is also not Microsoft Defender for Endpoint, which Microsoft’s FAQ calls a business and enterprise product.

If you decide a paid extra is a real job

Keep one real-time engine. Open a paid page only if you named an extra Defender does not include.

• Cleanup or a first-year suite on one household PC: TotalAV plans (paid link; confirm the renewal). If you install it, uninstall or disable the other real-time AV.
• US identity monitoring: Norton LifeLock plans (paid link). That is not a second antivirus.
• A suite some households pick when they want extras plus one live engine: Bitdefender plans (paid link).
• Many phones and PCs on one bill: McAfee plans (paid link; confirm the device limit).
• Home Wi-Fi extras after the router is locked: Avast plans (paid link).

Read the extras guide before you click. Buying nothing is still valid. Defender alone is the default if antivirus on this Windows PC is the only job.

FAQ

Do I need Malwarebytes if I already have Microsoft Defender?

Not as a second real-time product. Microsoft says you do not need another real-time antivirus or antispyware product. An occasional on-demand scan is optional.

Can I keep Malwarebytes Premium and Defender real-time both on?

No. That is two live engines. Microsoft recommends you do not run other antivirus or antispyware products at the same time as Windows Defender.

Is a one-time Malwarebytes scan OK?

Yes, if real-time protection in Malwarebytes is off (or you close it after the scan). Microsoft allows on-demand scanners such as Microsoft Safety Scanner next to a live product for the same reason: they run when asked.

Will Defender turn back on if I uninstall Malwarebytes?

Microsoft says if you do not have another security product, or it is expired, Defender turns on automatically. Confirm in Windows Security after you uninstall.

Is this the same article as “Is Microsoft Defender enough”?

No. That page is enough vs buying extras. This page is stacking two live scanners. Link: Is Microsoft Defender enough.

Does CISA say I must buy a third-party antivirus?

No. CISA tells you to use the native antivirus on the device, keep the OS and apps updated, and periodically confirm the scanner is still running.