Its a program that shows you an image of a stripping woman, and asks you to read captchas.
For every successfully read captcha, you will be rewarded with another photo.
The captchas are actually real ones coming from the yahoo signup process. So basically dumb users will be doing slave work for spammers.
The program is not widespread, but it has been spotted and I'm sharing the discovery because I think its interesting.
Here is the full article.
EDIT: forgot to copy the address :-)
http://news.bbc.co.uk/2/hi/technology/7067962.stm