Port Reporter is a windows service that logs all TCP and UDP port usage on any Windows system (Windows XP, 2003, 2000). These details can be analysed to find issues, such as malware on your system. This tool rocks!
The tool generates detailed log information about the usage of every network port by a system over time, and as such can generate a lot of log data. To help you analyse the log files, Tim has also produced a neat analysis tool, Port Reporter Parser which produces a wealth of summary information.
You can download Port Logger, and the port reporter parser tool, from Microsoft. Each of these are self extracting archives containing the setup programs. You have to manually configure the start up of the service.
For an outline of the tool, see Tim Rains' WebLog article about the tool. You can also see KB 837243 which describes this tool and the generated log files in more detail.
The tool has a bunch of little niggles, but it still rocks! Using it on my main workstation showed nothing bad (thankfully),but did reveal a couple of services that could be turned off. All in all, well worth the download and time to install and configure.