multiple addon using the same name found!

I have that message in the user preferences. I checked the system_info.txt but could not find any info in it.
how can I find out what is double and where ? Also how do I know which addon to keep and which to delete if I have installed a double?

Also what is the process of installing an addon from a zip and a py file ? Is it copied to a folder, or a copy placed somewhere?
I found “user scripts: ‘/home/yves/.config/blender/2.74/scripts’” on my system Linux Ubunti 11.04 but is it that ressource that is used or the one from the installation?