Today (2012-06-28) we are rolling out an unusually large security update. The update is necessary to fix known vulnerabilities. Unfortunately, the change has a small chance of breaking customer-compiled C extensions. We did our best to retain binary compatibility but we cannot guarantee it in every single case.
We ask all developers that have installed C extensions to verify that their programs are still starting up correctly. If not, a simple recompile should be sufficient to fix the problem.