Console Message: "kernel: Sandbox: net.conceited.Ru System Policy: deny(1) mach-priv-task-port 391"
This is indeed Rubbernet as @unknowndomain mentions - I was getting a flood of messages that caused 100% CPU for syslogd, visible in Console.
Since Conceited have gone out of business, here is how to uninstall Rubbernet:

open the Rubbernet .plist file that was launching the daemon, which should be /Library/LaunchDaemons/net.conceited.RubbernetDaemon.plist
ensure Launchd doesn't restart the Rubbernet process with launchctl unload -w /Library/LaunchDaemons/net.conceited.RubbernetDaemon.plist
kill the Rubbernet process via Activity Monitor, or using ps aux and kill
remove /Library/PrivilegedHelperTools/net.conceited.RubbernetDaemon (mentioned in the plist)
remove the plist -
rm /Library/LaunchDaemons/net.conceited.RubbernetDaemon.plist
remove the app - delete Rubbernet.app from /Applications

Writing this up because of the large number of &quot;Uninstall Rubbernet&quot; spam content sites that are promoting easy uninstall tools.  It should not be this hard to remove Rubbernet.
Background: launchctl stack