"An article filed on Thursday by The Associated Press reported the presence of a “previously unknown group calling itself the black block.” The article continued, “Wearing black masks and waving black banners, it warned the Muslim Brotherhood of using its ‘military wing’ to put down protests.”
Although largely new in Cairo, the term “black bloc” has been used for years in the United States and Europe to describe a tactic commonly used by anarchists and anticapitalists during large-scale political demonstrations that occasionally devolve into street fights with the authorities." (picture from As-Safir)