GEN:SID 1:245
Message DDOS mstream handler ping to agent
Summary This event is generated when an mstream handler attempts to identify active agents.
Impact Severe. If the listed source IP is in your network, it may be an mstream handler.  If the listed destination IP is in your network, it may be an mstream agent.
Detailed Information The mstream DDoS uses a tiered structure of compromised hosts to coordinate and participate in a distributed denial of service attack.  There are "handler" hosts that are used to coordinate the attacks and "agent" hosts that launch the attack.  A handler can probe to see if an agent is active by sending it a UDP packet to destination port 10498 with a string of "ping" in the payload.
Affected Systems Any mstream compromised host.
Attack Scenarios A mstream handler may probe to see if an agent is active.
Ease of Attack Simple. mstream code is freely available.
Corrective Action Perform proper forensic analysis on the suspected compromised host to discover the means of compromise.

Rebuild a confirmed compromised host.

Use a packet-filtering firewall to block inappropriate traffic to the network to prevent hosts from being compromised.
Additional References CVE:
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2000-0138
Rule References cve: 2000-0138