I got errors on my Mac today complaining about IO.pm. I had just installed Parrot on the way to building up a Rakudo to work on, so I figured something in the still-not-ironed-out Parrot install had caused the problem. It looked like this: 

% perl -MIO
IO object version 1.22 does not match bootstrap parameter 1.23
at /System/Library/Perl/5.8.8/....

I just figured I'd reinstall the module.I tried to update IO.pm, but the CPAN shell uses IO, and so barfed. Had to install it manually by downloading a tarball (gasp!) and doing it manually. And then everything was fine.

And then my old colleague Ed Silva IMs me asking if I knew anything about it. I had to confess I was surprised to see he had the same problem.

And now Miyagawa, bless his heart, lays it all out for you in this blog post about the Mac OS X security update. Ooopsie!

Thanks to Miyagawa for explaining the problem.