See "Manually download the latest updates", and read the rest of the web page too. See if manually downloading the "Definitions" breaks the loop?
Malware Protection Center
http://www.microsoft.com/security/portal/definitions/adl.aspx?wa=wsignin1.0
Did anyone try my earlier suggestion to hide the update?
If you switch off Automatic Updates and set them up to not download and only notify you then it is possible to hide a troublesome update. After doing such a thing you may return to your normal Automatic Update settings.
Control Panel\All Control Panel Items\Windows Update\Change settings
Hide Windows 7, or 8, Updates that you do not Ever Want to Install
http://technet.microsoft.com/en-us/magazine/ff382716.aspx
This is the one update that I would hide if it was my decision (as it is the oldest update).
Definition Update for Windows Defender - KB2267602 (Definition 1.193.3002.0)