They cannot be killed easily. They also cannot be easily open-sourced as answered below. They were put on death roll. In the sense, that people with authority

They cannot be killed easily. They also cannot be easily open-sourced as answered below. They were put on death roll. In the sense, that people with authority deemed them rightly deserved to be killed. But any software that needs authority to be declared dead, certainly have a life of their own. One such case is when the practitioners see the software has great value and an inherent vitality to sustain itself, but were simply rejected by people with authority. Did you know that Borg itself were put on death roll once, by Google's most powerful technical authority? That history ruined my respect for many of the once-golden images. But in the end a great lesson that anything that is valuable, is also worth fighting for. Just an example of how ridiculous an authority could become, if allowed to be unchallenged. Even in technical sphere, where is thought to be more rationale.