BugTraq reports an issue exists in Internet Key Exchange (IKE) protocol which could cause a Windows 2000 host to stop responding. IKE contributes to the IPSec standard by providing additional features and by default listens on UDP port 500.
"If a user connects to port 500 on a Windows 2000 host running IKE, andproceeds to submit a continuous stream of packets, the target will consumeall available system resources. A restart of the system maybe required in order to regain normal functionality."
See more at http://www.securityfocus.com/bid/3652