Skip to main content

Disable Defender Antivirus "Block at First Sight" feature

Apply Now
Works with Windows 10 and 11Works with Windows Vista, XP, 7, 8, 10, 11, and Windows Server 2008 or newer.
  • Windows onlyThis script improves your privacy on Windows
  • Single actionThis page belongs to a script, containing basic changes to achieve a task.
  • Impact: Medium

    System Functionality / Data Loss Risk: Moderate

    This action improves privacy with minimal impact when you run the recommended script.

    This action improves privacy with some impact when you run the recommended script.
  • Batch (batchfile)These changes use Windows system commands to update your settings.
  • Administrator rights requiredThis script requires privilege access to do the system changes
  • Fully reversible

    You can fully restore this action (revert back to the original behavior) using this website.

    The restore/revert methods provided here can help you fix issues.

Overview​

This script disables the "Block at first sight".

Block at first sight is Defender Antivirus feature 1 2 3 4. It protects against threats by quickly detecting and blocking new malware 1. When Defender Antivirus encounters a suspicious file it can't identify, it consults its cloud protection backend 1. The cloud backend uses heuristics, machine learning, and automated analysis to identify malicious files 1. This back-end is part of Cloud Protection 1. It is also known as Microsoft Active Protection Service (MAPS) 1 2 3 or SpyNet 2.

This feature is enabled by default 4, depending on other configurations 1 2. The feature is included in Defender for Endpoint suite 1.

Automatically sending files to Microsoft's cloud 1 3 raises significant privacy concerns. This script improves your privacy by preventing automatic file uploads to Microsoft. It may also improve system performance by reducing background network activity.

However, disabling this feature may reduce your device and network protection levels 1 3. The Defense Information Systems Agency (DISA) recommends keeping this feature enabled for additional security 3.

Caution

This change enhances privacy but may reduce overall system security.

Technical Details​

This script configures the option by:

  • Using the Defender CLI to set the DisableBlockAtFirstSeen preference 4.
  • Configuring HKLM\Software\Microsoft\Windows Defender\SpyNet!DisableBlockAtFirstSeen to mimic the CLI. Tests indicate that the CLI sets this registry key.
  • Setting the registry key HKLM\Software\Policies\Microsoft\Windows Defender\SpyNet!DisableBlockAtFirstSeen to configure the group policy 2 3.
  1. Security Trade-off

    This action prioritizes privacy over certain security features. It's not recommended and should only be used by advanced users after understanding its implications.

    Increased Privacy

    Enhanced privacy through reduced data collection and tracking

    Decreased Security

    Some security features will be disabled or limited

    This script can be reversed, this action allows you to can restore the system security.

  2. Use with Caution

    This script is only recommended if you understand its implications.

    Some non-critical or features may no longer function correctly after running this script.

    This script can be fully reversed to restore changes if something goes wrong.

Sources
PrivacyLearn.com maintains strict sourcing standards for accuracy, integrity and up-to-date content. Our content relies on authoritative sources including vendor documentation, industry standards, and verified research. Learn more about our verification process and quality standards in our editorial standards page.

Apply Now​

Choose one of three ways to apply:

Download script​

Download and run the script directly
  • No app needed
  • Offline usage
  • Easy-to-apply
  • Free
  • Open-source
Help

How to apply or restore "Disable Defender Antivirus "Block at First Sight" feature" using script​

  • ≈ 2 min to complete
  • Tools: Web Browser
  • Difficulty: Simple
  • ≈ 5 instructions
  1. 1

    Download

    Download the script file by clicking on the   Apply protection  button above.
    Use   Undo protection button above to restore changes.
  2. 2

    Keep the file

    If warned by your browser, keep the file.
  3. 3

    Open

    Open the downloaded file.
  4. 4

    Exit

    Once it's done, press any key to exit the window.
  5. 5

    Restart

    Restart your computer for all changes to take effect.

Apply with privacy.sexy​

Guided, automated application with safety checks
  • Recommended for most users
  • Includes safety checks
  • Free
  • Open-source
  • Popular
  • Offline/Online usage
Open privacy.sexy
Help

How to apply or restore "Disable Defender Antivirus "Block at First Sight" feature" using privacy.sexy​

  • ≈ 3 min to complete
  • Tools: privacy.sexy
  • Difficulty: Simple
  • ≈ 4 instructions
privacy.sexy is free and open-source application that lets securely apply this action easily with more advanced options.
  1. 1

    Open or download

    Open or download the desktop application
  2. 2

    Choose script

    1. Search for the script name: Disable Defender Antivirus "Block at First Sight" feature
    2. Check the script by clicking on the checkbox.
  3. 3

    Run

    Click on ▶️ Run button at the bottom of the page.

    This button only appears on desktop version (recommended). On browser, use 💾 Save button.

Run commands​

Copy and run commands manually Requires technical knowledge
Apply changes
PowerShell -ExecutionPolicy Unrestricted -Command "$propertyName = 'DisableBlockAtFirstSeen'; $value = $True; if((Get-MpPreference -ErrorAction Ignore).$propertyName -eq $value) { Write-Host "^""Skipping. `"^""$propertyName`"^"" is already `"^""$value`"^"" as desired."^""; exit 0; }; $command = Get-Command 'Set-MpPreference' -ErrorAction Ignore; if (!$command) { Write-Warning 'Skipping. Command not found: "^""Set-MpPreference"^"".'; exit 0; }; if(!$command.Parameters.Keys.Contains($propertyName)) { Write-Host "^""Skipping. `"^""$propertyName`"^"" is not supported for `"^""$($command.Name)`"^""."^""; exit 0; }; try { Invoke-Expression "^""$($command.Name) -Force -$propertyName `$value -ErrorAction Stop"^""; Set-MpPreference -Force -DisableBlockAtFirstSeen $value -ErrorAction Stop; Write-Host "^""Successfully set `"^""$propertyName`"^"" to `"^""$value`"^""."^""; exit 0; } catch { if ( $_.FullyQualifiedErrorId -like '*0x800106ba*') { Write-Warning "^""Cannot $($command.Name): Defender service (WinDefend) is not running. Try to enable it (revert) and re-run this?"^""; exit 0; } elseif (($_ | Out-String) -like '*Cannot convert*') { Write-Host "^""Skipping. Argument `"^""$value`"^"" for property `"^""$propertyName`"^"" is not supported for `"^""$($command.Name)`"^""."^""; exit 0; } else { Write-Error "^""Failed to set using $($command.Name): $_"^""; exit 1; }; }"
:: Set the registry value: "HKLM\Software\Policies\Microsoft\Windows Defender\SpyNet!DisableBlockAtFirstSeen"
PowerShell -ExecutionPolicy Unrestricted -Command "$registryPath = 'HKLM\Software\Policies\Microsoft\Windows Defender\SpyNet'; $data = '1'; reg add 'HKLM\Software\Policies\Microsoft\Windows Defender\SpyNet' /v 'DisableBlockAtFirstSeen' /t 'REG_DWORD' /d "^""$data"^"" /f"
:: Set the registry value: "HKLM\Software\Microsoft\Windows Defender\SpyNet!DisableBlockAtFirstSeen"
PowerShell -ExecutionPolicy Unrestricted -Command "function Invoke-AsTrustedInstaller($Script) { $principalSid = [System.Security.Principal.SecurityIdentifier]::new('S-1-5-80-956008885-3418522649-1831038044-1853292631-2271478464'); $principalName = $principalSid.Translate([System.Security.Principal.NTAccount]); $streamFile = New-TemporaryFile; $scriptFile = New-TemporaryFile; try { $scriptFile = Rename-Item -LiteralPath $scriptFile -NewName ($scriptFile.BaseName + '.ps1') -Force -PassThru; $Script | Out-File $scriptFile -Encoding UTF8; $taskName = "^""privacy$([char]0x002E)sexy invoke"^""; schtasks.exe /delete /tn $taskName /f 2>&1 | Out-Null; $executionCommand = "^""powershell.exe -ExecutionPolicy Bypass -File '$scriptFile' *>&1 | Out-File -FilePath '$streamFile' -Encoding UTF8"^""; $action = New-ScheduledTaskAction -Execute 'powershell.exe' -Argument "^""-ExecutionPolicy Bypass -Command `"^""$executionCommand`"^"""^""; $settings = New-ScheduledTaskSettingsSet -AllowStartIfOnBatteries -DontStopIfGoingOnBatteries; Register-ScheduledTask -TaskName $taskName -Action $action -Settings $settings -Force -ErrorAction Stop | Out-Null; try { ($scheduleService = New-Object -ComObject Schedule.Service).Connect(); $scheduleService.GetFolder('\').GetTask($taskName).RunEx($null, 0, 0, $principalName) | Out-Null; $timeout = (Get-Date).AddMinutes(5); Write-Host "^""Running as $principalName"^""; while ((Get-ScheduledTaskInfo $taskName).LastTaskResult -eq 267009) { Start-Sleep -Milliseconds 200; if ((Get-Date) -gt $timeout) { Write-Warning 'Skipping: Timeout'; break; }; }; if (($result = (Get-ScheduledTaskInfo $taskName).LastTaskResult) -ne 0) { Write-Error "^""Failed, due to exit code: $result."^""; } } finally { schtasks.exe /delete /tn $taskName /f | Out-Null; }; Get-Content $streamFile } finally { Remove-Item $streamFile, $scriptFile; }; }; $cmd = '$registryPath = ''HKLM\Software\Microsoft\Windows Defender\SpyNet'''+"^""`r`n"^""+'$data = ''1'''+"^""`r`n"^""+''+"^""`r`n"^""+'reg add ''HKLM\Software\Microsoft\Windows Defender\SpyNet'' `'+"^""`r`n"^""+'    /v ''DisableBlockAtFirstSeen'' `'+"^""`r`n"^""+'    /t ''REG_DWORD'' `'+"^""`r`n"^""+'    /d "^""$data"^"" `'+"^""`r`n"^""+'    /f'; Invoke-AsTrustedInstaller $cmd"
Help

How to apply or restore "Disable Defender Antivirus "Block at First Sight" feature" using commands​

  • ≈ 2 min to complete
  • Tools: Command Prompt
  • Difficulty: Medium
  • ≈ 3 instructions
 View step-by-step guide with screenshots
  1. 1

    Open Command Prompt

    Open Command Prompt as Administrator.
  2. 2

    Copy code

    Copy the code:
    Copy Apply Code Copy Revert Code
  3. 3

    Paste & run

    Paste the commands into Command Prompt and press Enter to run.

    Some changes require a system restart to take effect

Similar Guides​

Wider Goal​

Guides below includes this guide to achieve a wider goal.

See other more general settings that includes this one as one of its actions.

These plans combine multiple privacy settings, including this one, for stronger protection.

This category contains scripts that disable or limit Microsoft Defender's cloud-based protection features. Microsoft Defender's cloud protection is also known as M...
Visit category page

Same Goal​

Other guides in Disable Defender Antivirus cloud protection 

See settings that are in the same category as this guide.

Using other actions in the same category may help you achieve your goal better.

Disable Defender Antivirus "Extended Cloud Check" feature
Disable Defender Antivirus aggressive cloud protection
Disable Defender Antivirus cloud-based notifications
Disable Defender Antivirus cloud protection reporting
Disable Defender Antivirus automatic file submission to Microsoft
Disable Defender Antivirus real-time security intelligence updates

About the Creators​

These people have authored this documentation and written its scripts:

  • Avatar of undergroundwires. The creator of PrivacyLearn and privacy.sexy. Black and white portrait showing a person wearing a polka dot tie and suit jacket, reflecting the professional expertise behind the privacy protection tools.
    • Certified security professional
    • 7+ years experience securing banks
    • Open-source developer since 2005
    • EU advisor, Public Speaker, Moderator
    • Hundreds across the globe
    • Testers, reviewers, developers
    • Companies, military agencies
    • Community since 2017
About Us

Reviewed By​

This guide has undergone comprehensive auditing and peer review:

  • Expert review by undergroundwires​

    • Verified technical accuracy and editorial standards
    • Assessed system impact and user privacy risks

  • Public review by large community​

    • Privacy enthusiasts and professionals peer-reviewed
    • Millions of end-users tested across different environments

History​

We continually monitor our guides, their impact and all other privacy options. We update our guides when new information becomes available. On every update, we publicly store who made the change, what has been changed, why the change was made and when the change was made.

Review Change History Our Change Process