1. Restore your console to its factory settings. This will delete all of the data on your console, so make sure you back up your game saves before you do this.
2. Delete your Call of Duty: World at War profile. To do this, go to the "My Xbox" section of the Xbox dashboard, select your profile, and then select "Delete Profile."
3. Reinstall Call of Duty: World at War. This will overwrite the hacked files with the original game files.
4. Update your Xbox 360 console to the latest firmware version. This may help to fix any security issues that could have been exploited by the hacker.
If none of these methods work, you may need to contact Microsoft customer support for assistance.