Spam. Everyone hates spam, unless you are the ones behind it. Many tools and plugins have been developed to fight spam in the past. Some works brilliantly while others may not fair that well.
Math anti-spam function (an example is the Did you pass Math plugin) works by requesting the person commenting to answer a “simple” mathematical question. An example would be “What is the sum of nine and two”. Simple right?
However, I read that some spam tools were able to bypass these math anti-spam functions. I guess that is why some developers have raised the level of complexity by asking more complex math question.
Honestly, I read in the past that a blogger stopped using the math anti-spam tool (the one where you sum up two numbers together) because at least one of his readers had problems answering them. The math question above can still be considered as simple to most of us but does this mean that your readers have to be at least of a high school qualification before they can comment in your blog?
“What is the chemical that is produced by mixing 4ml of X, 2.5g of Y and 10ml of Z?”