GEN:SID 1:366
Message ICMP PING *NIX
Summary ping is a standard networking utility that determines if a target host
is up. This rule indicates that the ping originated from a host running
Unix.
Impact Information Disclosure. Ping can be used as a reconnaissance tool.
Detailed Information ping sends an ICMP Echo Request packet to an IP address.  If a host is
up at that address it will reply with an ICMP Echo Reply.  The reply
includes the data portion of the echo packet.  The data included in the
Echo Request varies across different operating system implementations.
Affected Systems All
Attack Scenarios An attacker will often ping a machine to make sure it is up before
attacking.
Ease of Attack Simple.
Corrective Action ICMP packets can be blocked with a packet filtering firewall.
Additional References