The most effective way to assure yourself that no-one can use your PC in your absence is to block it, and with MRT Lock you can do so in just one click.
To unblock MRT Lock just press a combination of keys you previously decide. You can program it to also automatically block during a set amount of time, in seconds, you specify.
If the user wants, they can indicate that the program starts when the PC starts, and only a set of key combinations can unblock it. MRT Lock is simple, totally free and hardly consumes system resources.