Word(s) for a person who degrades other people's work/efforts anonymously.
meta:
I really want to know since this sickness is wide-spread across Internet.
To me, this is a filthy mix of cowardice and total lack of integrity. One word that is close (too strong, though) is 'terrorist', lowlifes, hiding behind masks or anonymous accounts, disseminating hate. It is interesting whether such a word exists because calling names is so infectious, and the immediate reaction usually is to name back, here lies the trickiness of this non-human act – to drag you in the pit.
Best Answer
In internet jargon, there is keyboard warrior. These people hide behind their keyboards in total anonymity and show their hatred towards other users in online platforms.
Urbandictionary has a lot of entries for this term but I'm surprised that Oxford Dictionaries includes a definition also: