I have been using , PC tools Registry Mechanic , For about five years , on five different machines , Never had any adverse effects, I have run this on some computers that have never used this software and their machine was running slow and random BSOD's Results 1,200, or more errors first run , than keep running it until it comes uo SYS is clean. No more BSOD and quicker start up . I know some techies say don't use it ,but I use every day no iLL effects???