Microsoft admitted to quiet security patching. We knew many years ago that they did this: not counting extra vulnerabilities that were found internally or by researchers contracted to work for them. For closed source, single vendor software, this isn't too big of a deal - it's not like the user has a choice if they need to update some application to address one critical vulnerability or 20.
When you look back, before they admitted to this practice, Microsoft actively used vulnerability counts in reports as a tool to discredit the security of open source distributions. Famously even Steve Ballmer participated in counting vulnerabilities using candy.
In other news, the Red Hat Enterprise Linux 4 risk report we release each year has been published (PDF). This whitepaper looks at the state of security for the first five years of Red Hat Enterprise Linux 4 from its release on February 15th, 2005. It includes metrics, key vulnerabilities, and the most common ways users were affected by security issues.
"Red Hat knew about 52% of the security vulnerabilities that we fixed in advance of them being publicly disclosed. The average time between Red Hat knowing about an issue and it being made public was 22 days (median 10 days).... A default installation of Red Hat Enterprise Linux 4 AS was vulnerable to 14 critical security issues over the entire five years. "