Fix: Microsoft Teams Update Blocked by ThreatLocker

A business user contacted us because Microsoft Teams kept showing a banner asking them to update, but every time they tried, the update would fail with a blocked notification from ThreatLocker. They had restarted their computer multiple times, but the same thing kept happening. We identified that ThreatLocker, an application control security tool installed on their managed PC, was blocking the new Teams update files. We guided the user to submit a request through the ThreatLocker notification, approved it from our end, and the update completed successfully.

Symptoms

When attempting to update Microsoft Teams on a managed device, the update fails and a ThreatLocker notification appears:

Application Blocked - The application has been blocked from executing. Please contact your IT department.

You may also notice:

• Teams displays a persistent banner prompting you to update
• The update appears to start but then fails immediately
• Restarting your computer does not resolve the issue
• The ThreatLocker notification appears each time the update is attempted

Cause

ThreatLocker is an application control (allowlisting) tool used on managed business endpoints. It works by maintaining a list of approved applications and blocking anything that is not explicitly allowed.

When Microsoft Teams pushes an update, the new executable files have different hashes and signatures compared to the previously approved version. Because these updated files are not yet on the approved list, ThreatLocker treats them as unknown applications and blocks them from running.

This is expected behaviour from ThreatLocker. It is doing exactly what it is designed to do: preventing unapproved executables from running on your computer. The issue is not a fault with Teams or ThreatLocker, but rather that the updated files need to be approved before they can execute.

Resolution

Option 1: Request Access Through ThreatLocker (Recommended)

1. When the ThreatLocker “Application Blocked” notification appears, click the notification.
2. A ThreatLocker dialog will open. Click Request Access.
3. Add a brief note such as “Teams update blocked, please approve” and submit the request.
4. Your IT team will receive the request in the ThreatLocker portal and approve the new Teams files.
5. Once approved, restart Microsoft Teams and the update should complete successfully.

Option 2: Reinstall Microsoft Teams

If the request access method is not available or the issue persists, you can reinstall Teams:

1. Open Settings > Apps > Installed apps on your computer.
2. Search for Microsoft Teams and click Uninstall.
3. Go to microsoft.com/microsoft-teams/download-app and download the latest version.
4. Install the downloaded file. The fresh installation will be the latest version and should be approved by your IT team’s ThreatLocker policies.

Important Notes

• ThreatLocker blocking an application update is normal and expected behaviour on managed devices. It means your endpoint security is working correctly.
• Do not attempt to disable or uninstall ThreatLocker. It is a critical security tool that protects your device from unauthorised software.
• If you see ThreatLocker blocking other applications during updates, the same “Request Access” process applies.
• Your IT team may proactively approve common application updates to reduce these prompts in the future.

Related Resources

• Microsoft - Get clients for Microsoft Teams
• ThreatLocker Documentation
• Microsoft - Troubleshoot Teams installation issues
• ThreatLocker Blocked an App? How to Request Approval
• Fix: New Teams Won’t Open or Load Messages (Reset Teams)
• Fix: FortiClient Install or Update Blocked by ThreatLocker

If you need help with application control or Teams update issues, get in touch with our team.