Mac OS X Security Update 2009-001 breaks Perl;
Perl breakage only occurs if you’re running Leopard (Mac OS X 10.5), you’re using the Perl distro baked into the OS, and you’ve updated the distro via CPAN (Comprehensive Perl Archive Network), a widely-used collection of existing Perl modules.
This would indicate that Apple’s security update reverts Mac Perl to an older IO object incompatible with newer CPAN modules. “The Security Update brings (old) IO.bundle with version 1.22 but your IO.pm has been updated to the latest 1.23 on CPAN shell. (But hey, 1.23 was released in 2006…Why do you bring that ancient version back, Apple!?),” …