NURCaptcha inserts a reCAPTCHA on the Register Form of your site to protect it against spambots.
If you was facing a greater number of spambot registrations than the figures you see now in the log counter, that means the plugin is doing its job perfectly. Almost all the spambots give up their attack when confronted by the reCaptcha challenge, so they come and go silently. These bots may not trigger the counter, but they will not get inside your site walls, either.
That is the main target of any captcha plugin: to catch bots and allow human beings to pass by. In order for it to somehow prevent you against badly mooded human intruders, their data (email & IP) are checked against trustable anti-spam databases (from plugin version 3.0.0 on).
These people will leave their track on the log file. So check the log file regularly to see if there is someone you'd like to bring into your subscribers database. The log will give you that person's username, email and date/time when he tried to register and failed. Then it's up to you to add that user manually or send him an email with directions for an effective registration. The most common problem that keeps good people outside is not due to the reCaptcha, but illegal (non ASCII) characters in usernames. That is why we added a help box to the register form.
On december, 2014, Google released a new version of reCAPTCHA. This new version is more friendly to the user and far more advanced in technology, if compared to the former version. If you are upgrading from an older version of Skt NURCaptcha, we strongly reccomend you to enable the new version, in the settings page of this plugin. If you have this version of the plugin in a fresh installation, the new version of thr reCAPTCHA is enabled by default. The only reason to keep both versions of reCAPTCHA is to allow old users to prepare for the change. We don't know how long will it take till Google disable the old reCAPTCHA's API, so an automatic (forced) transition to the new version will be provided in future releases of this plugin.