OS X Yosemite Security and Privacy Guide
Please do not enable "stealth mode" in the ALF.  This violates applicable standards, impedes system and network management, and provides no additional security (as anyone with nmap can readily verify).  Hosts are required to respond to unicast ICMP echo requests, period [0].  No exceptions.<p>[0] <a href="https://tools.ietf.org/html/rfc1122#page-42" rel="nofollow">https://tools.ietf.org/html/rfc1122#page-42</a>