There are all sorts of mobs on the internet.
There are political mobs who defend their favorite ideology/party/candidate while attacking opponents.
There are sports mobs who defend their favorite team. I’ve been on the receiving end of no small amount of vitriol from fans of the NDSU Bison athletic teams, which has a few times tempted me to contact law enforcement.
There are mobs which form around bands or actors or other celebrities, but perhaps the scariest sort of mob are those which form around a supposed pursuit justice.