To stay up-to-date with the security fixes you should subscribe to receive GLSAs and apply GLSA instructions whenever you have an affected package installed.
http://www.gentoo.org/security/en/index.xml

Abstract . This document outlines a method for receiving regular notifications via email of Gentoo Linux Security Advisories (GLSA) related to the specific packages you have ...
http://en.gentoo-wiki.com/SECURITY_Getting_GLSAs_by_Email

GLSA 200810-02 (High): portage - 24/10/2008 00:00 GMT Portage: Untrusted search path local root vulnerability
http://gentoo-portage.com/GLSA

distribute GLSAs in the portage tree (completed) release a beta version of the GLSA handling code in gentoolkit (in progress) move dependency handling code from emerge to portage.py ...
http://www.gentoo.org/proj/en/portage/glsa-integration.xml