This is done most likely to force a reboot or dupe the user into restarting the machine. Terminating csrss.exe and wininit.exe, for instance, will cause a blue screen of death (BSOD). Terminating winlogon.exe will prompt the user to log in again, while terminating lsass.exe will cause a reboot. KillDisk also uses the ExitWindowsEx function to forcefully restart the machine