Please install this update to your Windows computers today. You can do so by choosing "Windows Update" from your Start menu, or visiting http://www.windowsupdate.com/ in Internet Explorer. (That's the only time I'm ever going to tell you you should be using IE instead of another web browser.) Or, if you don't have control over the Windows computer you use at work, please ask your IT staff to install the update today.
I've already patched the Sony Vaio I have at work. Please patch your computer now. Thanks.
More details are available here. The upshot is that unpatched Windows computers could be easily taken over by an attacker, who could then use your computer to attack other computers.
(Details added based on discussion in comments. Yes, I take this seriously. I'm not a Windows security expert, but Windows security experts whose opinions I trust are concerned enough about this vulnerability that I felt it worth my time and energy to spread the word.)