There is a program called VBLock. It looks really good, and it has WAY more features. It is really good. I haven’t tried it, but I think it should actually work. Check it out on http://vblock.neocities.org

@macgregor.daniel: Confirmed. Whoa, that's a major league bug.

What happens if the computer is locked with this software and *then* you plug in a monitor?

@framitz: I think the fact that the screen isn't really locked (Ctrl+Alt+Del kills the program) would be the bigger security violation.

aah, useless with dual monitors.

I just tried this and it does not work with multiple monitors. the secondary monitor is still wide open. I can click on anything and type.

This is dangerous. Don't trust 3rd party lockers, it just expands the attack surface. Stick to the trusty WIN+L to lock your screen.