I know this sounds a little confusing, however, WinReducer has never "removed" Windows Defender, at least to my knowledge and so your observation is somewhat accurate. Go to Windows Defender and try to use it or change any of the settings and you will find that it is actually dysfunctional. This, however, is ONLY true with the more stable Windows 10 1511 build. If you have the Insider Preview installed then when it goes to install more current updates you can kiss all the changes WREX100 made goodbye. The bottom line is, for the purposes of testing WREX100 using Insider Previews is not so much a dangerous endeavor, however, be ready for lots of surprises of which they have nothing to do with WREX100.