UNIX "ShellShock" Bug
Sunday, September 28, 2014 at 7:53AM 
A bug was discovered in the BASH shell for UNIX late last week. What does this mean for us Mac users? Mac OS X is built on UNIX and includes that BASH shell. That "shell" or "command prompt" is a piece of software that allows the Mac to be controlled without the use of the graphic interface.
This bug (CVE-2014-6271) can be exploited by an outside source requesting some basic information about your system, which could allow a hacker complete control. Apple released a statement Saturday saying "the vast majority of Mac computer users were not at risk from the bug." The reason for this is that your Mac is, by default, configured with all WAN services disabled and would not respond to any requests from the outside. This is not the case for most Servers, or for anyone who has altered their Mac system.
Apple is working on a patch to the OS which should be run as soon as it is made available.