Microsoft has a perhaps little-known RSS feed for security-related advisories. I say perhaps little-known because I added it to my Bloglines list of feeds, and it reported that this feed had 1 subscriber. Compare that to Eric Meyer's 245 subscribers or Aaron Swartz's 1292 subscribers.
So either this RSS feed is new, not-widely known, or no one seems to care about it.
I hope it's new, because it seems quite useful and should be standard reading for web designers regardless of what operating system or browser you use.
And if you haven't heard, Microsoft just issued some sort of a double-secret-probation high security alert today for Internet Explorer. Something about "could allow hacker to gain complete control over infected computer."
Not to worry, the target computer would have to have Visual Studio, Office 2003, or Office XP already installed -- and what are the odds of that? (This post added from Firefox browser.)