For nearly 10 years, Microsoft has posted patches (software updates) to fix security flaws in various Microsoft products on the second Tuesday of each month, informally known as “Patch Tuesday”.
Read Microsoft’s Security Bulletin Summary for August 2013 at http://technet.microsoft.com/en-us/security/bulletin/ms13-aug
The August 2013 bulletin announces the availability of a “critical” Cumulative Security Update for Internet Explorer for versions 6, 7, 8, 9 and 10 for Windows desktop clients running Windows XP, Windows Vista, Windows 7 and Windows 8, various Windows server versions and Windows RT.
Also, there is a separate “critical” update for Windows XP and Windows Server 2003
The “critical” rating means that vulnerabilities exist in the aforementioned products that could allow for remote code execution without user interaction, meaning malware can be installed on your system just by by visiting a web page or opening a document file.
So run Windows Update ASAP!