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Microsoft has confirmed in their IE blog (http://windowsteamblog.com/ie/b/ie/archive/2011/12/15/ie-to-start-automatic-upgrades-across-windows-xp-windows-vista-and-windows-7.aspx) that users will be silently updated to the latest version of their IE browser to improve security.
Windows XP users will be upgraded to Internet Explorer 8 and Windows Vista & 7 users will be upgraded to Internet Explorer 9.
Users can opt out on this silent update by turning automatic updates off, but I recommend that you should always upgrade to the latest version as it adds new features and fixes bugs and you'll always be supported.