Rollback

      Within the context of cryptocurrency & blockchain, the term rollback is used to refer to the reversal of network activity. Rollback is typically only used for Proof-of-Work environments. 

     Whenever some drastic event occurs, such as the the breaching of a centralized exchanges security systems and digital assets are stolen, It is theoretically possible to persuade the community to accept a “rollback” of events that happened on the digital assets chain. If the rollback is agreed upon then all of the networks activity since the attack is “re-winded” and all activity is undone. 

     Rollback’s are tricky because between the attack and the moment of rollback, many blocks can be mined and those mined blocks each cost the miners non-refundable energy expenditure; not to mention that each block contains activity of network participants who would have all of their activity erased. Rollbacks are a great fallback mechanism in global crises (total network takeovers) but for individual hacks they do not serve as ideal solutions.