Use PowerShell’s built-in Update-MpSignature cmdlet to request the latest Microsoft Defender Antivirus definitions, then use Get-MpComputerStatus to confirm the version, update time, age, and out-of-date flag. The commands apply to supported Windows 10, Windows 11, and Windows Server installations where Defender is present and permitted to update.
What the PowerShell update actually does
Microsoft Defender Antivirus relies on antimalware definitions, also called security intelligence, to recognize current malware patterns. The Defender PowerShell module exposes one cmdlet for requesting an update and another for inspecting the resulting state. Update-MpSignature asks an update service for newer definitions; it does not replace the Defender engine, change real-time-protection settings, or scan every file on demand.
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The update source is normally selected by the computer’s configured SignatureFallbackOrder. When no fallback order is configured, Microsoft documents Microsoft Update Server followed by the Microsoft Malware Protection Center (MMPC). Managed computers can instead be directed to an internal WSUS definition server or another approved source, so a successful command depends on policy, connectivity, and the services allowed by your organization.
Before you run the command
Confirm that Defender is the relevant antivirus
These cmdlets report on Microsoft Defender Antivirus. On a personal computer, Defender may be the active protection provider. On a managed computer, another endpoint product, a security baseline, or a policy can change which provider is active or whether Defender updates are allowed. The command can still be present even when an administrator has restricted its use.
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Use the right PowerShell window
Open PowerShell from the Start menu or Windows Terminal. A standard window is sufficient on many installations, but local policy or the specific Defender operation can require elevation. If the command reports access denied, policy restrictions, or a service-control error, close the window and open PowerShell with Run as administrator, then retry.
Expect a network-dependent operation
Definitions must be obtained from an allowed update source. A proxy, firewall, offline device, VPN policy, WSUS configuration, or temporarily unavailable service can prevent new files from arriving even though PowerShell itself is working correctly.
Step-by-step: request a Defender definition update
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Open PowerShell. Elevate the window if your local policy requires administrator rights or if an unelevated attempt fails.
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At the prompt, run:
Update-MpSignatureThe cmdlet requests the latest definitions available through the configured source order. It normally returns control to the prompt after the request completes; the absence of a long progress display is not, by itself, proof that the device is current.
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Allow the operation to finish. Do not close the PowerShell window or disconnect the computer from its required network while the request is running.
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Continue with the verification command in the next section. A current signature version and recent timestamp are more useful than assuming that a command which returned without an obvious error changed the device.
Choose an update source explicitly
Most users should allow the configured fallback order to decide. Explicit selection is useful when diagnosing a source problem, testing a managed configuration, or following an administrator’s instructions. Microsoft documents four accepted values for the -UpdateSource parameter.
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| Source value | When it is appropriate | What to verify |
|---|---|---|
InternalDefinitionUpdateServer |
A managed environment that distributes definitions through its internal update server, commonly WSUS. | The computer can reach the internal server and policy permits that route. |
MicrosoftUpdateServer |
You need to request definitions from Microsoft Update explicitly instead of relying on the configured order. | Windows Update connectivity, proxy rules, and organizational approval. |
MMPC |
An administrator has approved Microsoft Malware Protection Center as the requested source. | Outbound access to the service and any endpoint policy governing fallback. |
FileShares |
Your organization maintains an approved definition package on a file share. | Share permissions, path configuration, and the policy that defines the share. |
For the documented Microsoft Update example, run:
Update-MpSignature -UpdateSource MicrosoftUpdateServerDo not use an explicit source merely to bypass enterprise controls. If a device is configured for an internal server, forcing a public source may violate policy or produce a result that is not representative of the organization’s update process.
Verify the definition version and freshness
After the request, query Defender’s status rather than relying on the command prompt alone:
Get-MpComputerStatus | Select-Object AntivirusSignatureVersion, AntivirusSignatureLastUpdated, AntivirusSignatureAge, DefenderSignaturesOutOfDateThe four selected properties answer different questions:
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- AntivirusSignatureVersion identifies the definition package currently installed.
- AntivirusSignatureLastUpdated shows when Defender recorded the most recent signature update.
- AntivirusSignatureAge reports the age of the installed signatures, which helps reveal a device that has stopped receiving updates.
- DefenderSignaturesOutOfDate is the status flag indicating whether Defender considers the signatures stale.
A healthy result normally has a recent update timestamp, a low signature age, and an out-of-date flag of False. “Recent” is relative to your organization’s update policy and the device’s connectivity; there is no universal timestamp that proves every computer is current.
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Display only the installed version
For a quick focused check, request the version property alone:
Get-MpComputerStatus | Select-Object -ExpandProperty AntivirusSignatureVersionUse the full four-property query when troubleshooting because a version without its timestamp and age does not show whether updates are still arriving.
Capture a complete status record
When you need broader diagnostics, run:
Get-MpComputerStatusThis returns the antimalware status object, including the signature fields above and other Defender state. Save the output only according to your organization’s handling rules; status data can reveal device and security configuration details.
Foreground, background, and remote execution
The basic command runs in the current PowerShell session on the local computer. The same Defender cmdlets expose optional parameters for administration scenarios, but each changes how you monitor and troubleshoot the operation.
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| Approach | Command pattern | Use it when | Operational trade-off |
|---|---|---|---|
| Local, foreground | Update-MpSignature |
You are updating the computer you are using and can wait for completion. | Simplest to observe; the session remains occupied while the request runs. |
| Local, background job | Update-MpSignature -AsJob |
You need the update request to run as a PowerShell background job. | You must monitor the job and retrieve its result; starting a job does not prove that definitions were downloaded. |
| Remote computer | Update-MpSignature -CimSession $session |
You administer another Windows computer through an established CIM session. | Requires remoting configuration, authentication, firewall access, and permissions on the target. |
| Remote status check | Get-MpComputerStatus -CimSession $session |
You need to verify the target after a remote request. | The returned properties describe the remote device, not the computer running your console. |
-AsJob and -CimSession are optional administration features. Do not add them to a one-off local update unless you specifically need asynchronous execution or remote scope.
Monitor a background job
If you started the update with -AsJob, inspect the job from the same PowerShell session:
Get-JobWhen the job reports completion, retrieve its output and errors:
Receive-Job -Id <job-id>Replace <job-id> with the numeric identifier returned by Get-Job. Finish by running the status query against the same computer; job completion is only an execution event, while the signature properties show the resulting Defender state.
Use an existing CIM session safely
A remote command requires a valid CIM session variable. For example, an administrator might create a session using the organization’s approved computer name and credentials, then pass that session to both cmdlets. The exact session-creation method depends on remoting policy, network topology, and authentication, so do not assume that a remote command will work merely because the local command does.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Why an update can appear not to work
The signature age does not change
Run the full status query and compare AntivirusSignatureLastUpdated, AntivirusSignatureAge, and DefenderSignaturesOutOfDate. If all remain unchanged, the request likely could not obtain a newer package, the device already had the newest package available from its source, or policy blocked the operation.
The computer is managed by WSUS or another internal policy
Do not assume that a public Microsoft source is the correct fix. A managed endpoint may be required to use InternalDefinitionUpdateServer, and its fallback order can be centrally controlled. Contact the administrator responsible for endpoint or Windows Update policy when the internal route is unavailable.
Network or proxy access is blocked
Check whether the computer can reach its approved update service from the same network context used by Defender. A browser test is not a substitute for validating the service, proxy, and policy path used by the antimalware component. Test again after restoring the required connection, then inspect the timestamp and age fields.
PowerShell reports access or policy errors
Retry in an elevated window if permitted. If the error persists, endpoint policy, tamper protection, disabled services, or a centrally managed configuration may be responsible. Do not disable security controls just to force an update; escalate the exact error text and the status output to the administrator.
The command exists but Defender is not active
The Defender module can be installed even when another antivirus provider is controlling protection or an administrator has disabled parts of Defender. Check the broader output from Get-MpComputerStatus and follow the device owner’s security policy before changing providers or services.
Automate a repeatable update-and-check routine
For a local maintenance script, keep the update and verification as separate stages so that the result is observable:
Update-MpSignature
Get-MpComputerStatus | Select-Object AntivirusSignatureVersion, AntivirusSignatureLastUpdated, AntivirusSignatureAge, DefenderSignaturesOutOfDateRun this only in environments where scripting is allowed. Record the returned properties in the organization’s approved monitoring system rather than treating a successful PowerShell process exit as a compliance signal. If the routine runs remotely, create and validate the CIM session first, pass it to both commands, and distinguish connection failures from a Defender result showing stale signatures.
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- It does not perform a full malware scan. Use the separate Defender scan controls when scanning is required.
- It does not guarantee that the newest definitions are available if the approved source, network, or policy is unavailable.
- It does not override WSUS, endpoint management, tamper protection, or other administrative controls.
- It does not require a third-party physical product; the workflow uses Windows’ built-in Defender PowerShell module.
- It does not make an illustrative version or timestamp from documentation a universal current value. Always read the values returned by the device you are checking.
Recommended workflow for personal and managed PCs
Personal computer
- Open PowerShell, elevating only when required.
- Run the standard Defender signature-update cmdlet using the configured source.
- Query the four signature properties and confirm that the timestamp and age are current for your normal update policy.
- If the values remain stale, restore network access and retry before investigating software or service problems.
Organization-managed computer
- Identify whether policy requires an internal definition server or a specific fallback order.
- Run the update through the approved source, or allow the configured order to operate.
- Verify the local or remote status properties and retain the output according to administrative procedures.
- Escalate policy, service, permission, or connectivity errors instead of bypassing controls.
This gives you both halves of a reliable update: a request for new definitions and a device-side check that shows what Defender actually installed.
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