HSR

Apple has the capcha of the hardware business.
Suppose I have connected a key logger to your computer. Maybe a physical one or maybe a software one but it is there and copying everything you type. Suppose that I could use the internet and, armed with all this info and a black heart, get into your computer remotely and do malice.
In previous iterations of OSX I would log on or have a screensaver on and move a mouse or stroke a screen or whatever to release the screensaver. It would be password protected and a screen would pop up waiting for the typed secret password. Too bad about the key stroke logger. It can be reversed, and do all this in the background. Too bad for you.
In Lion, when a screensaver is on it has to be turned off. There is a little outline of the big x for close. You move over to get focus and click or tap. Now the password box comes up but the system does not give it focus. It takes input from hardware to get the password in.
Getting a software solution for a hardware problem makes this a very tough security challenge. Better luck sticking to cracking the captchas.