Sentence:  The dirty secret of the internet is that all this distraction and interruption is immensely profitable. Web companies like to boast about [...], or offering services that let you "stay up to date with what your <WSD>friends</WSD> are doing",...and so on. But the real way to build a successful online business is to be better than your rivals at undermining people's control of their own attention. 
Meaning of the word marked with <WSD> tags:  A person with whom one is vaguely or indirectly acquainted