[njharman]

In usa everything that is copyrightable, becomes copyrighted at moment it is created. For instance that sentence, and this on, are protected works owned by me. The only reAson HN can legally use then is cause I gave them license, buried somewhere in Eula/site terms of use.

Also, an architecture is not copyrightable. Maybe patentable. Copyrights protect specific expressions, not a general idea, plan, or architecture. At least not yet thankfully I haven't seen anyone try to argue an unrelated software doing same thing is a derivative work.

[mavelikara]

But Twitter has a patent pledge with its engineers [1]:

    The IPA is a new way to do patent assignment that 
    keeps control in the hands of engineers and designers. 
    It is a commitment from Twitter to our employees that 
    patents can only be used for defensive purposes. We will
    not use the patents from employees’ inventions in 
    offensive litigation without their permission. What’s
    more, this control flows with the patents, so if we sold
    them to others, they could only use them as the inventor 
    intended.

[1]: https://blog.twitter.com/2012/introducing-the-innovator-s-pa...