I was in the defendant class for one of these Silicon Valley film anti-poaching lawsuits. :) And I agree that companies, including the one I worked for, shouldn’t be able to agree to prevent hiring from each other. The main problem this caused was it made it harder for any individual to leave one company for another, with no poaching involved, and because of that (it was argued) it suppressed the general competitiveness and salaries of the employees.

Do keep in mind that this case (companies agreeing they won’t hire from each other) is a bit different from an angry employee leaving and soliciting some friends to go with him to a new company. Like I said, it might be perfectly legal, and yet still cause you serious trouble if you do it. Some people have ended up a lot more frustrated after leaving because of things they did on the way out. It can work out well if you’re really in a position to start your own company and fight like the Traitorous Eight, but for most devs who just want a job, making huge waves on exit is pretty dangerous. Don’t take my word for it though.

Also is the word here really "illegal" or more like a breach of contract? I am not saying doing the opposite of what you signed is legal per-se, my point is that I am not sure if there are actual written laws saying you can't poach.

At least in my experience people agree to that, and it's usually when exiting a company, not when joining. As in "you agree not to initiate poaching up until 12 months after leaving the company".

Didn't know about that, thanks!

Yeah, many times. I'm always joining a new contract with at least some people from the previous ones. Never had anyone care in the slightest - it's not like the person would've stayed anyways. Why is it their business at all? The person doesn't belong to them.