GEN:SID 1:241
Message DDOS shaft synflood
Summary This event is generated when a DDoS Shaft handler agent launchs a SYN flood against a target.
Impact Attempted DDoS. If the listed source IP is in your network, it may be a Shaft agent.  If the listed destination IP is in your network, your host may be a target of a DDoS SYN flood.
Detailed Information The Shaft DDoS uses a tiered structure of compromised hosts to coordinate and participate in a distributed denial of service attack. Agents are hosts that are directed to launch attacks.  One type of attack that may be launched is a SYN flood of a target.  The SYN packets have a telltale initial sequence number of 674711609.
Affected Systems Any Shaft compromised host.
Attack Scenarios A Shaft agent may attack a target using a SYN flood.
Ease of Attack Simple. Shaft 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 Arachnids:
http://www.whitehats.com/info/IDS253

Miscellaneous:
http://biocserver.cwru.edu/~jose/shaft_analysis/

Rule References cve: 2000-0138
arachnids: 253