A friend created a website for my granddaughter that included a guest book for people to leave messages.

It has quickly become bombarded with the sort of messages found in spam, many of which are inappropriate for children. Is there any way to stop these messages?
David Housley

Spam comments left on website guest books are an increasing problem online and are often generated automatically by computer programs.

Thankfully this automation also gives the answer to the problem, which is to add some form of question that only a real person can answer.

This is often in the form of an image of distorted text or sometimes a simple sum. These questions are called Captcha, an acronym for Completely Automated Public Turing test to tell Computers and Humans Apart.

The exact version of Captcha you need depends on the software used to create the website. You can find more information here, along with plugins for popular website software, such as Wordpress.

It is also crucial to realise that adding a Captcha question may make the website difficult or impossible for people with disabilities to use the website. There is more information in this article by the organisation responsible for web standards.