4.5 installer by default was GDR but I patched it with KB2519265 to change it to take LDR updates (these are non security bug fixes,) with 4.5.1 (it changed) there are 2 installers with 2 sets of files netfx_Full_GDR_x*.msi andnetfx_Full_LDR_x*.msiIf you ONLY care about security updates you would choose the GDR, but if you want security updates and "hotfixes" from the microsoft knowledge base you should pick LDR (these will fail to install if you install the GDR)If you are using the default EXE and you want to install the LDR branch you need to use <ndp451_installer>.exe /trainswapBTWLDR = Limited Distribution Release (same as QFE = Quick Fix Engineering) GDR = General Distribution Release More info