CAPTCHAs are a ubiquitous feature of the internet. Many websites use then to distinguish between real human beings and software attempting to add content to the site. Usually the real human beings are the ones you want to permit, while the software is attempting to add spam to the site, so it's a useful problem to solve. Essentially, a CAPTCHA is a mini Turing Test to try to distinguish between humans and machines.
I came across an article pointing out that we could harness spammers to help solve artificial intelligence problems to advance the field of research. Essentially, spammers have a lot of financial incentive to solve the problems. When they solve these problems, we simply present them with new unsolved problems.
This situation is hilariously clever. It's also the natural progression of the CAPTCHA arms race. So, the next time you get annoyed by spammers on websites that are protected by CAPTCHAs, think about the spammer's contribution to computer science!