Today Microsoft issued a Security Advisory describing a vulnerability in the Microsoft XML component. We discovered this vulnerability—which is leveraged via an uninitialized variable—being actively exploited in the wild for targeted attacks, and we reported it to Microsoft on May 30th. Over the past two weeks, Microsoft has been responsive to the issue and has been working with us. These attacks are being distributed both via malicious web pages intended for Internet Explorer users and through Office documents. Users running Windows XP up to and including Windows 7 are known to be vulnerable.
As part of the advisory, Microsoft suggests installing a Fix it solution that will prevent the exploitation of this vulnerability. We strongly recommend Internet Explorer and Microsoft Office users immediately install the Fix it while Microsoft develops and publishes a final fix as part of a future advisory.