Issue: I would like to block certain member groups from appearing on the active user list.

Method: You can do that one of two ways. One is to make the user group color the same as the background color of the active user display in the board statistics. This allows you to highlight the name and see it if you want. The other way is to prevent the name from displaying at all. This is handy if you have user groups for bots or banned members that you would rather not see on the active user list.

Here's how to block the name. You will know that members of this group are signed in because a comma will appear when they are online. Admins will still be able to see IP addresses, but members will only see the comma.

ACP > Users and Groups > Manage User Groups > Edit group> Global Settings:
Online List Format [Prefix]

Online List Format [Suffix]

To just make the name invisible against the background, do this:

(Example:<span style='color:red'>
addresses, but members will only see the comma.

ACP > Users and Groups > Manage User Groups > Edit group> Global Settings:
Online List Format [Prefix]

Online List Format [Suffix]