The installation of the
Security Update 2006-007 apparently changes the way SSL certificates are validated by WebKit-based applications. If you ever changed the certificate security policies, you may be unable to connect to SSL sites with Safari. A notable example is
https://mail.google.com/mail/.
The fix is to revert to the default certificate security policy by removing the file ~/Library -> Preferences -> com.apple.security.revocation.plist.
Note that if you are not experiencing any connection problems, you do not need to perform this action!