Apple Security Update 2015-006 is recommended for all users and improves the security of OS X. For detailed information about the security content of this update, please visit: http://support.apple.com/kb/HT1222
The download link above is for OS X 10.Mavericks; see Related Links for additional security updates. Also please understand that the security updates mentioned here were applied to OS X 10.10 Yosemite in the OS X 10.10.4 operating-system update.
Note: Information about the security updates contained in this update can be found here. https://support.apple.com/en-us/HT205031