Otherwise, a process may run at startup, trying to open the Software Update. If not successful, it waits and then repeats itself every 40 seconds; it will spam the system.log (as well as burn a few processor cycles, I guess). YMMV.
Details
I wanted to set up a very restricted user account, for a kiosk.
Using the admin account, I created a guest account and set it as the auto-login. I also used the Accounts pane -> Capabilities to turn off the Guest user's ability to "open all system preferences" and also checked "Use Only These Applications", selecting "System Preferences" and my one app.
Because I had already set these restrictions, when I logged into the machine as the Guest user, I was unable to access the "Software Update" pref pane, so I could not uncheck "Automatically check for updates with you have a network connection" as the guest user.
I noticed ( by logging into the machine as 'admin' via ssh, then tail -f 'ing the system.log file ) that entries like the following kept showing up:
Jul 25 20:13:16 hostname open: CG/CPS: The application with pid 3938 is not in the list of permitted applications and so has been exited.
Jul 25 20:13:55 hostname open: CG/CPS: The application with pid 3939 is not in the list of permitted applications and so has been exited.
Jul 25 20:14:34 hostname open: CG/CPS: The application with pid 3940 is not in the list of permitted applications and so has been exited.
I suspected software update, but to confirm this, I connected as the guest user and tried running software update myself:
[hostname] guest% /usr/bin/open /System/Library/CoreServices/Software Update.app
and was able to watch the same error lines appear in the system.log (as the admin) each time I tried the command.

