Data Protection and Security

I

Introduction to Information Security

I.II

Common Information Security Targets

Practice

Several companies (Yahoo, Google, etc.) offer free email services. These services all suffer from an attack called ‘bots’ signing up thousands of email accounts in every minute, which might affect the availability to ordinary users. The solution is to come up with a mechanism that can distinguish between a computer and a human so that the registration is only possible for human but not computers.

A captcha (an acronym for "completely automated public turing test computers and humans apart") exactly does this. Below you see an example for captchas, a distorted text which can be read by humans but not computers. Of course this is not necessarily absolute, a development in artificial intelligence might enable also the computers to read the text.

Figure I.II-I

This captcha of "smwm" obscures its message from computer interpretation by twisting the letters, and adding a background color gradient.