bcworks, it seems that WordPress does have such a feature installed as-standard. I vaguely remember having this issue on a website a few years ago (abandoned project due to a change of career path), I'm also having this issue just now with a site I'm working on. When I first load the login page it takes me straight to the "Are You Human?" Page claiming it's a popular page, this simply isn't the case as no one even knows I have this hosting account/domain let alone that the website itself exists. Ironically, after logging in I've been almost constantly loading the login page in another browser and I'm accessing it no problem without the "Are You Human?" Page showing so I'm unable to take a screenshot of it at this point. I can tell you however that it's a yellow page with a reCAPTCHA box.
Note that this started before I'd installed any plugins, only change I'd made on the first day was the theme (Tempera), however, as only the login.php page is showing this I highly doubt it's theme-related (and I know for sure it's not a server-side issue, I've asked the host).
Website in question is - http://altpro.theweare.net
Any ideas anyone?