#Requires -Version 5.1
<#
    JbTecWiz Support Centre -- generated fix script

    Fault : Microsoft Defender will not turn on
    Fix   : Find and remove the policy holding it off
    Source: https://jbtecwiz.com/support/win-sec-defender-off

    Run as     : Elevated PowerShell
    Expect     : 30 minutes
    Risk       : high
    Reversible : yes

    WHEN THIS IS THE RIGHT FIX
    No other antivirus was involved. Treat a machine that disabled its own
    antivirus as potentially compromised.

    HOW TO UNDO IT
    The policy values can be recreated, though on a managed machine they
    should be set by Group Policy rather than by hand.

    This script walks the fix one step at a time and asks before each
    one. Steps with no command are things you do yourself -- it prints
    those and waits. Run with -DryRun to print without executing.

    --------------------------------------------------------------------
    NO WARRANTY - USE AT YOUR OWN RISK

    This script is provided by JbTecWiz as-is and with no warranty of any
    kind, express or implied. You run it entirely at your own risk.

    JbTecWiz accepts no liability for any loss or damage arising from its
    use, including but not limited to data loss, downtime, or configuration
    changes that turn out to be wrong for your system.

    You are responsible for reading this script before running it, for
    satisfying yourself that it suits the machine in front of you, and for
    having a working backup first. Some steps cannot be undone.
    --------------------------------------------------------------------
#>

[CmdletBinding()]
param(
    # Print every step and command without running anything.
    [switch]$DryRun,
    # Do not ask before each step. Read the script first if you use this.
    [switch]$Unattended
)

$ErrorActionPreference = 'Stop'
$script:Failed = 0

function Write-Rule { param([string]$Text)
    Write-Host ''
    Write-Host ('-' * 70) -ForegroundColor DarkGray
    if ($Text) { Write-Host $Text -ForegroundColor Cyan }
}

function Show-Prose { param([string]$Text, [string]$Colour = "Gray")
    if (-not $Text) { return }
    $words = $Text -split "\s+"; $line = "  "
    foreach ($w in $words) {
        if (($line.Length + $w.Length) -gt 74) { Write-Host $line -ForegroundColor $Colour; $line = "  " }
        $line += "$w "
    }
    if ($line.Trim()) { Write-Host $line -ForegroundColor $Colour }
}

function Invoke-Step {
    param(
        [int]$Number, [string]$Do, [string]$Why,
        [scriptblock]$Command, [switch]$Manual, [string]$Shell = "powershell"
    )
    Write-Rule "  Step $Number of 5"
    Show-Prose $Do "White"
    if ($Why) { Write-Host ""; Show-Prose $Why "DarkGray" }

    if ($Manual) {
        Write-Host ''
        Write-Host '  -> Do this yourself, then press Enter to carry on.' -ForegroundColor Yellow
        if (-not $Unattended -and -not $DryRun) { [void](Read-Host) }
        return
    }

    Write-Host ''
    foreach ($l in ($Command.ToString().Trim() -split "`n")) {
        Write-Host ("    " + $l.Trim()) -ForegroundColor Green
    }
    Write-Host ''

    if ($DryRun) { Write-Host "  (dry run -- not executed)" -ForegroundColor DarkGray; return }
    if (-not $Unattended) {
        $a = Read-Host "  Run this step? [Y]es / [S]kip / [Q]uit"
        if ($a -match "^[Qq]") { Write-Host "  Stopped at your request."; exit 0 }
        if ($a -match "^[Ss]") { Write-Host "  Skipped." -ForegroundColor DarkGray; return }
    }
    try { & $Command }
    catch {
        $script:Failed++
        Write-Host ("  Step $Number failed: " + $_.Exception.Message) -ForegroundColor Red
        Show-Prose "The rest of the fix may depend on this. Read the write-up before carrying on." "Red"
        if (-not $Unattended) {
            $c = Read-Host "  Carry on anyway? [y/N]"
            if ($c -notmatch "^[Yy]") { exit 1 }
        }
    }
}

Write-Rule
Write-Host '  Microsoft Defender will not turn on' -ForegroundColor White
Write-Host '  Find and remove the policy holding it off' -ForegroundColor Cyan
Write-Host ''
Write-Host '  Risk: high   Reversible   30 minutes'
Write-Host ''
Show-Prose 'No warranty. Use at your own risk - JbTecWiz accepts no liability. Read it before you run it, and have a backup.' 'DarkYellow'
Write-Rule

if (-not $Unattended -and -not $DryRun) {
    $go = Read-Host '  Ready? [y/N]'
    if ($go -notmatch "^[Yy]") { Write-Host "  Nothing was changed."; exit 0 }
}

Invoke-Step -Number 1 -Do 'Look at the policy keys.' -Command {
    Get-ItemProperty 'HKLM:\SOFTWARE\Policies\Microsoft\Windows Defender' -ErrorAction SilentlyContinue
    Get-ItemProperty 'HKLM:\SOFTWARE\Policies\Microsoft\Windows Defender\Real-Time Protection' -ErrorAction SilentlyContinue
}

Invoke-Step -Number 2 -Do 'If DisableAntiSpyware or DisableRealtimeMonitoring is set to 1 on a machine with no management, that is a strong indication something set it deliberately.' -Why 'Disabling the antivirus by policy is one of the first things a lot of malware does. Turning it back on without investigating means it will simply be turned off again, or worse, will now be scanning a machine that is already compromised.' -Manual

Invoke-Step -Number 3 -Do 'Scan from outside the running system before re-enabling -- the Microsoft Defender Offline scan boots into its own environment.' -Command {
    Start-MpWDOScan
}

Invoke-Step -Number 4 -Do 'Remove the policy values.' -Command {
    Remove-ItemProperty 'HKLM:\SOFTWARE\Policies\Microsoft\Windows Defender' -Name DisableAntiSpyware -ErrorAction SilentlyContinue
    Remove-ItemProperty 'HKLM:\SOFTWARE\Policies\Microsoft\Windows Defender\Real-Time Protection' -Name DisableRealtimeMonitoring -ErrorAction SilentlyContinue
    gpupdate /force
}

Invoke-Step -Number 5 -Do 'Restart, confirm protection is on, and run a full scan.' -Command {
    Start-MpScan -ScanType FullScan
}

Write-Rule "  Confirm it worked"
Show-Prose 'Get-MpComputerStatus reports real-time protection enabled and a completed full scan.' 'White'
Write-Host ''
if (-not $DryRun) {
    Get-MpComputerStatus | Format-List RealTimeProtectionEnabled,FullScanEndTime,AntispywareEnabled
}

Write-Rule
if ($script:Failed -gt 0) {
    Write-Host ("  Finished with " + $script:Failed + " failed step(s).") -ForegroundColor Yellow
    Show-Prose 'Read the full write-up at https://jbtecwiz.com/support/win-sec-defender-off' 'Yellow'
} else {
    Write-Host '  Finished.' -ForegroundColor Green
}
Write-Host ''
Show-Prose 'To undo: The policy values can be recreated, though on a managed machine they should be set by Group Policy rather than by hand.' 'DarkGray'
Write-Rule