I had a Captcha pop up on here yesterday. Just clicked on a new thread and up it popped. Said due to unusual activity on my ISP, I needed to click the box to prove I'm not a robot. I ignored it at first but when I later looked at the forum again, on a different machine in a different place, the same Captcha appeared. So I clicked it and nothing bad seems to have happened. I've no idea what "unusual activity" might have been detected. What's going on?