Hi. I have a Desktop and Notebook with Windows 8.1 installed. Both with original license. Until August 6th, Windows Defender was updating their antivirus definitions. But, since that day it stopped updating. I tried WU and Windows defender but both doesn´t show any updates. Even manual updates downloaded from the Microsoft Website don´t install. It stopped updating with definition version: 1.155.1620.0. I didn´t use my notebook since August 4th.Today I updated my virus definitions and they were only updated to definition 1.155.1620.0. Since then, No more updates. But using Microsoft Security Essentials is updating normally. Can someone confirm if the virus definitions really stopped on August 6th? Here in Brazil I asked a friend who is also using Windows 8.1, and with him it stooped udating August 6th.