diff --git a/CHANGELOG.md b/CHANGELOG.md
index 38b9020..2ea5fcb 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -12,6 +12,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - The release workflow verifies the published Cloudsmith files at their
   actual download path (`raw/versions/<version>/<file>`), and a failed
   download is reported as a notice instead of a spurious checksum mismatch.
+- Windows activation retries transient access-denied errors from antivirus/
+  indexer scans instead of failing the install.
 
 ## [0.1.0] - 2026-07-30
 
diff --git a/install.ps1 b/install.ps1
index 3014d99..f0f2c9d 100644
--- a/install.ps1
+++ b/install.ps1
@@ -66,6 +66,33 @@ function Invoke-WithRetry {
     }
 }
 
+function Invoke-WithFilesystemRetry {
+    param(
+        [Parameter(Mandatory = $true)][scriptblock]$Action,
+        [ValidateRange(1, [int]::MaxValue)][int]$Attempts = 10,
+        [ValidateRange(0, [int]::MaxValue)][int]$DelayMilliseconds = 1000
+    )
+
+    # Windows Defender's real-time scan (or Search indexing) can briefly hold
+    # a handle on a just-extracted or just-touched directory, and
+    # Directory.Move fails outright if any handle is open. Retry only the
+    # transient access errors that pattern produces; anything else propagates
+    # immediately. The defaults match MSBuild's Copy task, which retries the
+    # same two exception types for the same reason.
+    for ($attempt = 1; $attempt -le $Attempts; $attempt++) {
+        try {
+            return & $Action
+        }
+        catch [System.UnauthorizedAccessException], [System.IO.IOException] {
+            if ($attempt -eq $Attempts) {
+                Write-Warning "Filesystem operation still blocked after $Attempts attempts $DelayMilliseconds ms apart; giving up"
+                throw
+            }
+            Start-Sleep -Milliseconds $DelayMilliseconds
+        }
+    }
+}
+
 function Test-DownloadUriAllowed {
     param([Parameter(Mandatory = $true)][string]$Uri)
 
@@ -482,17 +509,17 @@ try {
     # on wildcard characters like [ ] in the install root.
     $temporaryFinal = Join-Path $finalParent (".cloudsmith.new." + [Guid]::NewGuid().ToString("N"))
     $oldFinal = Join-Path $finalParent (".cloudsmith.old." + [Guid]::NewGuid().ToString("N"))
-    [System.IO.Directory]::Move($stagedDirectory, $temporaryFinal)
+    Invoke-WithFilesystemRetry { [System.IO.Directory]::Move($stagedDirectory, $temporaryFinal) }
 
     if (Test-Path -LiteralPath $binDirectory) {
-        [System.IO.Directory]::Move($binDirectory, $oldFinal)
+        Invoke-WithFilesystemRetry { [System.IO.Directory]::Move($binDirectory, $oldFinal) }
     }
     try {
-        [System.IO.Directory]::Move($temporaryFinal, $binDirectory)
+        Invoke-WithFilesystemRetry { [System.IO.Directory]::Move($temporaryFinal, $binDirectory) }
     }
     catch {
         if (Test-Path -LiteralPath $oldFinal) {
-            try { [System.IO.Directory]::Move($oldFinal, $binDirectory) } catch { Write-Warning "Failed to restore previous installation directory during rollback: $_" }
+            try { Invoke-WithFilesystemRetry { [System.IO.Directory]::Move($oldFinal, $binDirectory) } } catch { Write-Warning "Failed to restore previous installation directory during rollback: $_" }
         }
         throw
     }
diff --git a/tests/Install.Tests.ps1 b/tests/Install.Tests.ps1
index e268bbe..2826b49 100644
--- a/tests/Install.Tests.ps1
+++ b/tests/Install.Tests.ps1
@@ -46,6 +46,111 @@ Describe 'Cloudsmith CLI installer request metadata' {
     }
 }
 
+Describe 'Cloudsmith CLI installer activation retry' {
+
+    BeforeAll {
+        $installScriptPath = (Resolve-Path (Join-Path (Join-Path $PSScriptRoot '..') 'install.ps1')).ProviderPath
+        $tokens = $null
+        $errors = $null
+        $ast = [System.Management.Automation.Language.Parser]::ParseFile(
+            $installScriptPath,
+            [ref]$tokens,
+            [ref]$errors
+        )
+        if ($errors.Count -gt 0) {
+            throw 'install.ps1 has parse errors'
+        }
+
+        $retryFunction = $ast.Find({
+            param($node)
+            $node -is [System.Management.Automation.Language.FunctionDefinitionAst] -and
+                $node.Name -eq 'Invoke-WithFilesystemRetry'
+        }, $true)
+        if (-not $retryFunction) {
+            throw 'unable to find Invoke-WithFilesystemRetry'
+        }
+
+        . ([scriptblock]::Create($retryFunction.Extent.Text))
+
+        $script:RetryDefaults = @{}
+        foreach ($parameter in $retryFunction.Body.ParamBlock.Parameters) {
+            if ($parameter.DefaultValue) {
+                $script:RetryDefaults[$parameter.Name.VariablePath.UserPath] = $parameter.DefaultValue.Extent.Text
+            }
+        }
+    }
+
+    BeforeEach {
+        $script:AttemptCount = 0
+    }
+
+    It 'succeeds after transient UnauthorizedAccessException errors, retrying only as needed' {
+        $action = {
+            $script:AttemptCount++
+            if ($script:AttemptCount -lt 3) {
+                throw [System.UnauthorizedAccessException]::new("Access to the path 'C:\fake' is denied.")
+            }
+            return 'moved'
+        }
+
+        $result = Invoke-WithFilesystemRetry -Action $action -Attempts 5 -DelayMilliseconds 1
+
+        $result | Should -Be 'moved'
+        $script:AttemptCount | Should -Be 3
+    }
+
+    It 'succeeds after transient IOException errors' {
+        $action = {
+            $script:AttemptCount++
+            if ($script:AttemptCount -lt 2) {
+                throw [System.IO.IOException]::new('The process cannot access the file because it is being used by another process.')
+            }
+            return 'moved'
+        }
+
+        $result = Invoke-WithFilesystemRetry -Action $action -Attempts 5 -DelayMilliseconds 1
+
+        $result | Should -Be 'moved'
+        $script:AttemptCount | Should -Be 2
+    }
+
+    It 'rethrows once retries are exhausted' {
+        $action = {
+            $script:AttemptCount++
+            throw [System.UnauthorizedAccessException]::new("Access to the path 'C:\fake' is denied.")
+        }
+
+        { Invoke-WithFilesystemRetry -Action $action -Attempts 3 -DelayMilliseconds 1 } |
+            Should -Throw -ExceptionType ([System.UnauthorizedAccessException])
+        $script:AttemptCount | Should -Be 3
+    }
+
+    It 'does not retry unrelated exception types' {
+        $action = {
+            $script:AttemptCount++
+            throw [System.InvalidOperationException]::new('not a filesystem access error')
+        }
+
+        { Invoke-WithFilesystemRetry -Action $action -Attempts 5 -DelayMilliseconds 1 } |
+            Should -Throw -ExceptionType ([System.InvalidOperationException])
+        $script:AttemptCount | Should -Be 1
+    }
+
+    It 'keeps retrying by default for long enough to outlast an antivirus scan' {
+        $attempts = [int]$script:RetryDefaults['Attempts']
+        $delay = [int]$script:RetryDefaults['DelayMilliseconds']
+
+        (($attempts - 1) * $delay) | Should -BeGreaterOrEqual 9000
+    }
+
+    It 'rejects an attempt count that would skip the action' {
+        { Invoke-WithFilesystemRetry -Action { 'never runs' } -Attempts 0 -DelayMilliseconds 1 } |
+            Should -Throw
+        { Invoke-WithFilesystemRetry -Action { 'never runs' } -DelayMilliseconds -1 } |
+            Should -Throw
+    }
+}
+
 Describe 'Cloudsmith CLI installer (install.ps1)' -Tag 'Windows' -Skip:(-not $script:RunningOnWindows) {
 
     BeforeAll {