Comment by JangoSteve

This was a common approach called a "honeypot". As I recall, bots eventually overcame this approach by evaluating visibility of elements and only filling out visible elements. We then started ensuring the element was technically visible (i.e. not `display: none` or `visibility: hidden`) and instead absolutely positioning elements to be off screen. Then the bots started evaluating for that as well. They also got better at reading the text for each input.