Outlook Contacts are updating from the GAL

I receive a few complaints about a problem with Contacts being updated with content from the GAL:

My personal contacts are being updated with information in the GAL. I have a personal contact for another person that is in the GAL and it has slightly different information than is in the GAL but Outlook synchronized this contact information with the GAL and replaced the information in the contact with what is in the GAL. I never clicked on the "Update" button in the Contact ribbon, so is Outlook automatically doing this?

Yes, Outlook is doing it. Or, more accurately, Outlook's Social Connector (aka the People Pane) has an option to update contacts and its enabled.

When it's enabled, changes will be updated in the Contact with a "Details Changed" note added to the Notes field, at the end of any notes already in the Notes field.

To disable updating while keeping the People Pane active, go to People Pane button and select Account Settings to open the Social Connector settings, then click the Settings button to open the Update dialog.

The setting is stored in the registry:
HKEY_CURRENT_USER\​Software\​Microsoft\​Office\​Outlook\​SocialConnector\​RunAutomaticGALSync
Possible Values:
0 = Disable Sync
1 = Update without prompting
2 = Prompt before updating

Administrators can control it using Group Policy.

In Outlook 2016, disable the Social Connector add-in in File, Options, Add-ins.

Published May 13, 2011. Last updated on April 5, 2016.