This update is only for Leopard and Tiger users (Snow Leopard is not affected). I have not tested this on Tiger as I have no longer a machine with Tiger installed but I’ve tested the Leopard based update and that went without a problem. My production server and two of my test servers received the update and installed it without any problem.
Read more about the security update here.
n case of doubt, please make a full bootable disk image backup with Carbon Copy Cloner before you start. There are some people having reported problems with previous update so better be safe then sorry!