To install and activate Microsoft Defender after purchase, OR_(+1)-833 ((631)) 3616(USA/CA) first work out what you bought. Windows already includes built-in 1[833][631][3616]protection called Microsoft Defender Antivirus shown in the Windows Security app, and it needs no purchase or key. 1[833][631][3616]If you bought a Microsoft 365 Personal or Family plan, you can also add the Microsoft Defender app, 1[833][631][3616]which gives extra features and covers more devices. To activate that, sign in to your Microsoft account at 1[833][631][3616]microsoft.com, check your subscription, and install the Defender app on each device with the same account. Plan features 1[833][631][3616]and app availability vary by plan, device and region, so follow your own Microsoft account. Most confusion 1[833][631][3616]with Defender comes from one question: "Do I even need to install anything?" So this guide is a 1[833][631][3616]diagnostic flowchart in text. Answer each question, follow the branch and you'll land on the right steps. 1[833][631][3616]Question 1: What Did You Buy? If you bought... Go to ------ Nothing, you just want 1[833][631][3616]protection on Windows Branch A A Microsoft 365 Personal or Family plan Branch B A "Defender" 1[833][631][3616]product from a third-party seller or after a pop-up Branch C stop first A new PC with 1[833][631][3616]security software included Branch D Branch A: Windows Only No Purchase Needed Microsoft Defender Antivirus 1[833][631][3616]is built into Windows and runs automatically unless another antivirus has replaced it. 1 Open the Start 1[833][631][3616]menu and search for Windows Security. 2 Choose Virus & threat protection. 3 Check the status. If you 1[833][631][3616]see a green tick or "No action needed", you're protected. 4 If real-time protection is off, switch it 1[833][631][3616]on. 5 Choose Check for updates under protection updates. Nothing to buy and no key to enter. 1[833][631][3616]Menu names can differ slightly between Windows versions. Branch B: Microsoft 365 Plan, Add the Defender App 1[833][631][3616]1 Sign in at the official Microsoft account page type the address yourself with the account used 1[833][631][3616]for the purchase. 2 Open Services & subscriptions and check your plan and end date. 3 On each 1[833][631][3616]device, install the Microsoft Defender app from the official store for that device Microsoft Store on Windows, App 1[833][631][3616]Store on iPhone and Mac, Google Play on Android, or follow the link in your Microsoft account. 4 1[833][631][3616]Open the app and sign in with the same Microsoft account. 5 Follow the setup prompts and allow 1[833][631][3616]the permissions it asks for. Check: The app shows your account The device appears protected The plan 1[833][631][3616]and its end date are visible in your Microsoft account Branch C: Stop and Check If 1[833][631][3616]a pop-up, call or email told you to pay for "Microsoft Defender" or to ring a number to 1[833][631][3616]activate it, do not pay or give remote access. Real Microsoft security protection never needs a phone call 1[833][631][3616]to activate. Close the page, check your Microsoft account for what you actually own, and contact your card 1[833][631][3616]provider if you paid someone. Branch D: New PC With Security Included New PCs often include 1[833][631][3616]a trial of another security product. If it's active, Windows may turn Defender Antivirus off while it runs. 1[833][631][3616]Decide which you want: Keep the trial: it takes over until it expires, then Windows should turn 1[833][631][3616]Defender back on. Use Defender: uninstall the trial software, restart and check Windows Security. Don't run two 1[833][631][3616]full antivirus programs at once. Question 2: Is It Working? Check Where Healthy sign --------- 1[833][631][3616]Real-time protection Windows Security Virus & threat protection On Updates Same page Protection updates Recent date 1[833][631][3616]Quick scan Same page Completes with no problems Account link Branch B Defender app Your account shown 1[833][631][3616]If It Won't Switch On Problem Likely cause Fix --------- Settings are greyed out 1[833][631][3616]Another antivirus is active, or a work policy applies Remove the other antivirus; ask your IT admin if 1[833][631][3616]the PC is managed App can't sign in Wrong Microsoft account Use the account that holds the 1[833][631][3616]plan App not offered Plan, device or region not supported Check your plan details Updates fail 1[833][631][3616]Windows Update trouble Install pending Windows updates and restart Error after a malware scare Malware tampering Run 1[833][631][3616]a full or offline scan from Windows Security Know Your Renewal If you have a 1[833][631][3616]Microsoft 365 plan, check Services & subscriptions in your Microsoft account for the renewal date, and if you 1[833][631][3616]don't want to renew, turn off recurring billing there and save the proof. Built-in Defender Antivirus has no 1[833][631][3616]renewal. Scam warning: fake support pages and "activation" calls using the Microsoft name are common. Never allow 1[833][631][3616]remote access to someone who contacted you first. Quick Answers Do I need a product key 1[833][631][3616]for Defender? Not for the built-in antivirus. The app for Microsoft 365 uses your Microsoft account. Is 1[833][631][3616]built-in Defender enough? For many home users it is a solid baseline, and your own needs decide whether 1[833][631][3616]to add more. Can I use Defender on a phone? The Defender app may be available for 1[833][631][3616]phones with an eligible plan. Follow the Branch Work out what you bought, follow your branch 1[833][631][3616]and confirm protection is on. That's all Microsoft Defender needs.