A Security update has been issued for Leopard. It is recommended, of course, that all users update.
Security Update 2007-009 is recommended for all users and improves the security of the following components:
Core Foundation
CUPS
Flash Player Plug-in
Launch Services
perl
python
Quick Look
ruby
Safari
Samba
Shockwave Plug-in
Spin Tracer
For detailed information on this update, please visit this website.
UPDATE: The update is also for OSX 10.4 Tiger.