According to Apple, Leopard Security Update 2012-003 "disables versions of Adobe Flash Player that do not include the latest security updates and provides the option to get the current version from Adobe's website."
Also, the Flashback Removal Security Update "removes the most common variants of the Flashback malware. If the Flashback malware is found, a dialog will notify you that malware was removed. In some cases, the update may need to restart your computer in order to completely remove the Flashback malware."
Grab them both to secure your Leopard machine.