[gtremper]

I don't think they're breaking into their system at all. They're just abusing a public interface on their sight. A more apt analogy would be repeatedly calling their phone, or ringing their doorbell nonstop. Your analogy implies they are destroying GitHub's property, which they aren't.

[prawn]

Bit further than that. They're crowding your front porch with the explicit purpose of preventing any of your friends, family or customers actually getting to your front door. I think the intent is important to note. It's not a child who likes the sound of a doorbell, but an adult employed to achieve a very negative outcome.