Quicktime's latest version (7.6.7) is currently being exploited by a known bug. All IE users on Windows are affected. The majority of the readers of this blog are Chrome users (since most of you come here via the Chrome extension), but, for completeness, I thought I'd write about this. There's no fix yet, so the only way to keep yourself safe is to disable the Quicktime plug-in from IE.
References: http://www.securecomputing.net.au/News/231511,active-exploits-targeting-apple-quicktime-zero-day.aspx?eid=7&edate=20100909&eaddr=