Every organization is associated with a category and you can hide organizations by hiding the category that they belong to. This removes the organizations under a category from both the internal and external organization lists. It does not prevent users from accessing these portals. To begin, select the Admin dropdown in the top right of the screen, select your umbrella, choose the Organizations tab, then select the Categories tab from the menu on the left side of the page.
This page allows you to edit organization categories. There is a column labeled Hide orgs in search. Use the checkboxes under this column to determine which organization categories you'd like to hide.
Tip: Often times, you only want to hide one organization and you may not want to hide the entire category of organizations. In this case, consider creating a new organization category labeled "Hidden." You can then hide the organization by changing its category to "Hidden." Do this by going to the Admin dropdown in the top right of your screen, select your umbrella, choose Organizations, locate the org on this list, click on its profile picture, select View/Edit Full Profile, and change the organization's category.