Lashon Hara is not necessarily about revealing per se. It is the kind of talk that causes harm, or fights.
I know for a fact that someone who gets blasted by alias is affected as well. This is especially true if someone invested his personality, opinions and feelings into his online persona. Many here have virtual friends, acquaintances and think-alikes. Someone who attacks my personality is attacking me.
So, hurting and insulting someone online is Onaas Devarim, and therefore, causing others to do so in Lashon Hara.