CAPTCHA (Completely Automatic Public Turing to tell computers and Human Apart) has been developed to defend e-commerce systems from the attack of automatic scripts, spammers and bots; or to prevent worms on instant messaging (IM) (1). In this article, we review current CAPTCHAs and propose some improvement. A new scheme mouse intervention is presented with its strengths and weaknesses analysed. This scheme asks the users to solve a visual problem by using a mouse rather than typing the answer to a textbox.