I have windows vista and for quite some time updates are made more for windows defender. and to tell you, I uninstalled norton internet security and I installed avast ( lighter than the devil ) with an anti virus and spyware included and I also activated the Windows Defender antispyware in addition to that supplied by avast . but I can not update Windows Defender. My windows Defender is activated , but it is outdated . So now I want to know that how To manually Update Windows Defender Definitions ?