How to Fix MU Online DEP (Data Execution Prevention) Errors. If the game crashes on launch, shows a message like "This application has been closed to protect your computer", or stops unexpectedly on start — it may be due to Windows DEP blocking main.exe.

DEP is a Windows security feature that prevents harmful code from running — but sometimes it blocks older or modded game clients like MU.

What this guide does: Shows how to add MU's game file (main.exe) to DEP exceptions so Windows won't block it.

Step-by-Step: Add MU to DEP Exception List

1. Open System Properties: Press Windows Key + Pause/Break — or right-click This PC and choose Properties.
2. Click Advanced system settings (left sidebar).
3. Open Performance Settings: In System Properties, click Settings under the Performance section. Go to the Data Execution Prevention tab.
4. Enable DEP for All Programs Except Those You Select: Choose "Turn on DEP for all programs and services except those I select".
5. Add the MU Client Game File: Click Add…, browse to your MUOnline installation folder, select main.exe, click Open / Apply / OK.
6. Restart your PC.

Is This Safe? You are not disabling DEP for all programs — you are only excluding MU Online from DEP enforcement. This is a common fix for private server clients and older games.

Still Having Issues? Submit a ticket via the proper Discord channels.