Mac OS X 10.5.5 Update
The 10.5.5 Update is recommended for all users running Mac OS X Leopard and includes general operating system fixes that enhance the stability, compatibility and security of your Mac.
For detailed information on this update, please visit this website:
About Mac OS X 10.5.5
For explanation of what a SHA-1 digest is, please visit this website:
About SHA 1 digest
For detailed information on security updates, please visit this website:
About Security Updates