CAPTCHA at 6:33 PM

I came across this CAPTCHA method while reading Whirlpool today (original thread here). Interesting idea but a horrible implementation, I like it from the point of view of accessibility and usability but incredibly easy to defeat in its current implementation. As was pointed out in the thread in order to be effective both the span class and the separating character need to be random as well as probably the interval at which the hidden characters are inserted.