A lot of my recent work concerns how vulnerable the Internet is to bad code — in particular, how easily the generative PCs hooked up to it can find themselves reprogrammed for worse, in a heartbeat, either by drive-by downloads that sneak onto the machine or by code that the user affirmatively (but foolishly) asks to install.

CAPTCHAs are those squiggly words we’re asked to type in, designed to tell computers from humans on the Net, e.g.