ASP.NET AJAX Control Toolkit provided similar functionality since 2007. The corresponding component is called NoBot. http://www.ajaxcontroltoolkit.com/NoBot/NoB

ASP.NET AJAX Control Toolkit provided similar functionality since 2007. The corresponding component is called NoBot. http://www.ajaxcontroltoolkit.com/NoBot/NoBot.aspx http://www.ajaxcontroltoolkit.com/NoBot/NoBot.aspx "NoBot is a control that attempts to provide CAPTCHA-like bot/spam prevention without requiring any user interaction. This approach is easier to bypass than an implementation that requires actual human intervention, but NoBot has the benefit of being completely invisible." Works like a charm even now, 10 years later.