WHAT'S HAPPENING?
There have been reports that applying the latest Mac OS X (10.6.5) patch will cause your computer to become un-bootable IF you are running PGP WDE for the Mac.

WHY IS IT HAPPENING?
Apple overwrites the boot code file (that PGP had overwritten on its install for encryption key prompt) with a new one that does not know about encryption (from the support thread).

WHO IS AFFECTED?
Mac users running PGP WDE for the Mac.

WHAT DO YOU NEED TO DO?
The suggested workaround, at this time, is to decrypt the disk, install the update, and then re-encrypt the disk. Please contact your nearest Help Desk location for assistance.

WHO SHOULD YOU CONTACT FOR QUESTIONS?
The OIT Technology Support Center at 404-894-7173 or the TSO Help Desk (CCB 148, 404.894.7065, helpdesk@cc.gatech.edu).

Additional information is available at:

http://discussions.apple.com/thread.jspa?threadID=2643776&tstart=15