On Thursday, June 23, Apple released a security update for version 10.6 of OS-X – also known as Snow Leopard. Details about the new version are available from – http://support.apple.com/kb/HT4723
Update June 24
Some users have experienced problems when applying this update. For that reason, the recommendation from the AgriLife IT ISO is to wait until at least Monday, June 27 before applying the update.
Update 2011-06-24 16:30 UTC: As mentioned in the comments, some folks seem to have issues after applying the update and are subsequently unable to boot their machines. Until we get some guidance from Apple and/or figure out exactly what is causing the issue, I guess we need to exercise a bit of caution updating critical machines (based on your own definition of critical). There is a thread here discussing the issue, and another here suggesting the problem may be with PGP WDE, but I’ve heard from others who use PGP WDE who didn’t have any issues, so I’m still not sure what the problem is. Any of our users using PGP WDE who have successfully applied the update, please comment below or via the contact page.