CAPTCHAs (Completely Automated Public Turing Test to Tell Computers and Humans Apart) are one of the most widely used authentication mechanisms that help to prevent online service abuse. With the advent of mobile computing, mobile devices such as smartphones and tablets have be-come the primary way people access the Internet. As a result, increasing attention has been paid to designing CAPTCHAs that are mobile friendly. Although such CAPTCHAs generally show their ad-vantages over traditional ones, it is still unclear what the best practices are for designing a CAPTCHA scheme that is easy to use on mobile devices. In this paper, we present an exploratory study that focuses on developing a more holistic view of usability issues with interactive CAP-TCHAs to inform design guidance. This is done through investigating the usability performance of seven mobile friendly CAPTCHA schemes representing five different CAPTCHA types.