I am the admin of a closed forum for parents of disabled children. We do not want anybody to share information in the forum to external parts - in any way. Is there a setting to not show the "Share" link which has a dropdown menu with umpty alternatives?

Hello Vestihavet,

You're asking about the share button that displays in the topics, no ? If so, try adding the following code to your stylesheet.

Administration Panel > Display > Pictures and colors > Colors > CSS stylesheet

Code:

.addthis_button { display:none; }

Your advice was fine for the visible Share- button. However, in the Actions dropdown menu, there is another sharing button labelled "Send to a friend". Can that be removed too? 
(Yes, I know that anybody can copy text from a page and paste it into an email, but I don´t want it to be possible directly from the forum).

Add this to your CSS to remove the actions link :

Code:

a[href="javascript:showhide(document.getElementById('plus_menu'))"] { display:none; }