softwareupdated running at 100% CPU roughly every hour (Yosemite)
Hmm.  Try opening up terminal, and at the prompt, enter the command:


  $ softwareupdate -l &amp;&amp; sudo softwareupdate -i -a


That will tell the system to show you which updates need to be done, then run software update and install all of the updates it found.  See if it gives you any error messages; it may ask you to reboot right away, in which case do that.  Run the same command again after the reboot and see if it still finds updates to install or if nothing shows up.  If nothing shows up then it completed all the updates, and the problem hopefully goes away.  If not, let us know.