When on, ":autocmd", shell and write commands are not allowed in ".vimrc" and ".exrc" in the current directory and map commands are displayed. Switch it off only if you know that you will not run into problems, or when the 'exrc' option is off. On Unix this option is only used if the ".vimrc" or ".exrc" is not owned by you. This can be dangerous if the systems allows users to do a "chown". You better set 'secure' at the end of your ~/.vimrc then. This option cannot be set from a modeline or in the sandbox, for security reasons.

(default off)