Microsoft has yet to provide a solution for customers who can't connect to Microsoft Update to install last week's out-of-band patch KB 3011780
By Woody Leonhard Nov 25, 2014
The causes of the problem remain cloudy, but the symptoms are quite clear. Starting on Nov. 18, some Server 2003, Windows Home Server 2003, and Windows XP SP3 machines suddenly refused to connect to Microsoft Update. As best I can tell, Microsoft has not responded to the problem, not documented a workaround, and is basically doing nothing visible to fix it.
(Keep in mind that, although Windows XP is no longer supported, Security Essentials updates for XP still go through Microsoft Update, and all old patches for XP are still available -- when Microsoft Update is working, anyway.)
The main TechNet thread on the subject says the error looks like this:
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Error number: 0x80248015