SecurityAgent causing a freeze
It seems that the cable from the monitor to the power box wasn't fully connected. I noticed this a few days ago and made sure the cable was fully connected and I haven't had my issue since. At this point, it's just anecdotal evidence, but I wanted to log the answer in case others were having the same issue. Make sure your cables are fully connected!

UPDATE I received a new monitor for the holidays but it forced me to purchase a new monitor card, one that could handle Mini DisplayPort. Now that I have swapped out the monitor card, this problem is not happening anymore. So it seems it was related to the hardware, but more likely the card had some issue that was causing the problem.