Smart mobs sometimes are manipulated by the dispatchers who control the 'mobbing system' (i.e., those who own the contact list and the means to forward instant messages to a group) and are induced to cause distress and aggravation to individuals who have been targeted or singled out for whatever reason.
Flash mobs are a specific form of smart mob, originally describing a group of people who assemble suddenly in a public place, do something unusual and pointless for a brief period of time, then quickly disperse.