Stop ffap-machine-at-point from pinging random hosts

Having this on by default is highly problematic from a security and
privacy standpoint, as it risks having outgoing traffic that could
potentially reveal sensitive data (passwords, names, etc.).

It also seems to be causing issues for users, see e.g.
https://github.com/emacs-helm/helm/issues/648

* lisp/ffap.el (ffap-machine-p-known): Change default to 'accept'.

etc/NEWS

@@ -2042,6 +2042,12 @@ back the old behavior.
 This command prompts for a recently opened file in the minibuffer, and
 visits it.
 
+---
+*** 'ffap-machine-at-point' no longer pings hosts by default.
+It will now simply look at a hostname to determine if it is valid,
+instead of also trying to ping it.  Customize the user option
+'ffap-machine-p-known' to 'ping' to get the old behavior back.
+
 ---
 *** The 'run-dig' command is now obsolete; use 'dig' instead.
 

lisp/ffap.el

@@ -1,6 +1,6 @@
 ;;; ffap.el --- find file (or url) at point  -*- lexical-binding: t -*-
 
-;; Copyright (C) 1995-1997, 2000-2022 Free Software Foundation, Inc.
+;; Copyright (C) 1995-2022 Free Software Foundation, Inc.
 
 ;; Author: Michelangelo Grigni <mic@mathcs.emory.edu>
 ;; Maintainer: emacs-devel@gnu.org
@@ -394,7 +394,7 @@ Value should be a symbol, one of `ping', `accept', and `reject'."
   :safe #'ffap--accept-or-reject-p
   :group 'ffap)
 
-(defcustom ffap-machine-p-known 'ping	; `accept' for higher speed
+(defcustom ffap-machine-p-known 'accept
   "What `ffap-machine-p' does with hostnames that have a known domain.
 Value should be a symbol, one of `ping', `accept', and `reject'.
 See `mail-extr.el' for the known domains."
@@ -402,7 +402,8 @@ See `mail-extr.el' for the known domains."
 		 (const accept)
                  (const reject))
   :safe #'ffap--accept-or-reject-p
-  :group 'ffap)
+  :group 'ffap
+  :version "29.1")
 
 (defcustom ffap-machine-p-unknown 'reject
   "What `ffap-machine-p' does with hostnames that have an unknown domain.