While working on a new site I discovered, that reCaptcha - which used to be a rock solid part of the CMS since Joomla 1.7 - stopped working. Spent couple of hours googling around and checking and double-checking settings, just to discover, that Google, in his infinite wisdom, has changed things again without notice. The problem affects all Joomla versions from 1.7.1 to 3.2.0.
It's not a big deal - one can say - but lot of people is relying on these free services. The fix is simple, although needs some changes in the core code - so qualifies as a core hack. So, before you proceed, backup, and backup again, and check your backups ;)
When done, locate this file (exact location and the line number can vary, the below is for Joomla 2.5.1-2.1.16):
plugins/captcha/recaptcha/recaptcha.php
Open it, around line 25 locate these lines:
const RECAPTCHA_API_SERVER = "http://api.recaptcha.net";
const RECAPTCHA_API_SECURE_SERVER = "https://www.google.com/recaptcha/api";
const RECAPTCHA_VERIFY_SERVER = "api-verify.recaptcha.net";
Replace the first line's content to match the new location for reCaptcha API:
const RECAPTCHA_API_SERVER = "http://www.google.com/recaptcha/api";
const RECAPTCHA_API_SECURE_SERVER = "https://www.google.com/recaptcha/api";
const RECAPTCHA_VERIFY_SERVER = "api-verify.recaptcha.net";
Save it, and enjoy again the benefits of being protected again by reCaptcha!