There are many posts about DeepFreeze or ShadowUser in this forum, but I believe WinRollBack also deserves being mentioned, and appears to have at least one advantage over DP or SU: WINRollBack offers the novel facility to deactivate the protective effect during operating time in order to permanently define modifications without prior restart. It works as follows: To deactivate WinRollBack you must double-click the tray-icon and enter the correct password. The administration of WinRollBack will be opened. Inside the administration you must select the partition/drive and click the button "Deactivate". All changes on the selected partition will be made permanent on the selected partition/drive. Changes that where done since the last start of the PC will be made permanently. This in my view a huge advantage, as it removes the painfull steps of inactivation/reboot/trusted software installation/reboot/re-activation required for installing a trusted software.