graeme_p - 5:21 am on Oct 22, 2012 (gmt 0)
Sorry, no it is not always true any longer if you use the major desktop environments. If the outside executable you download is a .desktop file, then clicking on it in Gnome or KDE will execute it even if it does not have execute permission. See:
OK, that is a much smaller attack surface than the Windows equivalent, but it exists.