I have found the following plugin. Dropbox Folder Share which is licensed under the GNU General Public License.
In the plugin I have made some minor changes. mainly added my language. but i have also changed som other things.
How can I ensure that the plugin will not be updated. so I lose my changes
The nicest way to do it would be to hook into
'site_transient_update_plugins'
.A hacky way to do it would be to change the version number in the plugin to something ridiculously high, like
9999.999
.