The IE update (MS13-047) grapples with 19 vulnerabilities and covers all versions of IE, from IE6 to IE10, on all supported versions of Windows, from XP to RT. It's just the sort of thing that might be latched onto by hackers as part of drive-by-download attacks, based on malicious scripts on compromised websites, and therefore needs to be patched sooner rather than later.Details are posted on Microsoft's web site. Microsoft (and I) recommend that you have Windows Update enabled, which will download these automagically each month.
I also recommend (although Microsoft does not) that you look at using Firefox or Chrome browsers. Internet Explorer's security is a lot better than it used to be, but there's still quite a lot of legacy security fail built into it (*cough* ActiveX *cough*) that isn't in the other browsers. The Opera browser is also pretty good.