Rule:--Sid:231--Summary:This event is generated when a pong packet for the Trinoo (aka trin00) DDos suite is detected.--Impact:This may indicate a compromised system or be the prelude to aDistributed Denial of Service (DDoS) attack.--Detailed Information:Once a Trinoo client has been installed on a compromised machine and a master isready and listening, the master sends a "png" (ping) command to its drones in an attempt to enumerate the drone network. A functioning client will respond to port 31335/udp with the text "PONG".Once a machine becomes part of a trin00 network, a Denial of Service (DoS) is typically initiated against one (or more) victim machines.--Affected Systems: --Attack Scenarios:As part of a large scale attack against a machine or a network, anattacker will compromise large numbers of machines which will form thearmy that the trin00 master daemon will command.  The master daemontypically instructs the clients to send mass-quantities of packets toa set of victim hosts.  If the traffic is sufficient, the victimmachines will become resource deprived and thus endure a DoS condition.--Ease of Attack:Simple. Trinoo client and master programs are widely available.--False Positives:None Known--False Negatives:None Known--Corrective Action:Disconnect infected machine(s) from the network immediately.Use software to determine if a host has been compromised using arootkit.--Contributors:Original rule writer unknownSnort documentation contributed by Jon Hart <warchild@spoofed.org>Sourcefire Vulnerability Research TeamNigel Houghton <nigel.houghton@sourcefire.com>-- Additional References:SANS:http://www.sans.org/newlook/resources/IDFAQ/trinoo.htm--