Malformed input?

Came back to the computer after some time away, to find the sun shining full on the desk and part of the screen.  And, of course, the screen has blanked from lack of input during that time.

So, I pull the drapes forward to shade the screen–and the screen pops up, even though I haven’t touched the keyboard or the mouse.

Considering this, I realize that a) it’s an optical mouse, and b) it was on the part of the desk that was in the sun, and is now shaded when I pulled the drapes.

So, being a security geek, I start to wonder:

a) how the system interpretted that light?
b) how hard it would be to figure out how to get a laser to create specific “actions” on the computer?  (And if the optical sensor’s range is wide enough that you can do it with an IR laser, so the user doesn’t realize what you are doing?)