It's anecdotal, but since I added a little "What's two plus two" input box to my forms, we hardly get any more form spam. You could easily switch the question each time, although I haven't had the need to. We weren't getting hit once a minute, mind you, so you might be attracting a better class of bots . . . . On Tue, Jul 1, 2008 at 10:36 AM, MJ Ray <[log in to unmask]> wrote: > Thomas Dowling <[log in to unmask]> wrote: >> Does anyone know anything concrete about "cognitive" captchas? I've run >> into anecdotal support for things like: >> Enter the word "orange" <input name="foo"> > [...] >> Are these known to work? Or are they just clever guesses about what >> bots might not be able to figure out? > > There are mostly anecdotes because this stuff is hard to test > properly. I found they worked a little, but are just clever guesses. > > "3.1 Logic puzzles > > The goal of visual verification is to separate human from machine. One > reasonable way to do this is to test for logic. Simple mathematical > word puzzles, trivia, and the like may raise the bar for robots, at > least to the point where using them is more attractive elsewhere. > > Problems: Users with cognitive disabilities may still have trouble. > Answers may need to be handled flexibly, if they require free-form > text. A system would have to maintain a vast number of questions, or > shift them around programmatically, in order to keep spiders from > capturing them all. This approach is also subject to defeat by human > operators." > > Source: http://www.w3.org/TR/turingtest/#logic > > > As that last phrase hints, bots are not the only problem. See > http://www.schneier.com/blog/archives/2007/11/spammers_using.html > for example. > > > Hope that helps, > -- > MJ Ray (slef) > Webmaster for hire, statistician and online shop builder for a small > worker cooperative http://www.ttllp.co.uk/ http://mjr.towers.org.uk/ > (Notice http://mjr.towers.org.uk/email.html) tel:+44-844-4437-237 > -- Andrew Darby Web Services Librarian Ithaca College Library http://www.ithaca.edu/library/ [log in to unmask]