University researchers: There is evidence of pump-and-dump schemes prior to 51% crypto attacks

A group of university researchers published a study assessing the influence of 51% attacks on proof-of-work cryptocurrency prices. The study analyzes an exhaustive sample of 14 individual attacks on 13 cryptocurrencies. They are Bitcoin Gold, Bitcoin Private, Electroneum, Feathercoin, Karbo, Krypton, Litecoin Cash, MonaCoin, Pigeoncoin, Shift, Terracoin, Verge (attacked twice) and ZenCash (recently renamed to Horizen). Here is what the researchers found:

• 51% attacks on a blockchain show an immediate decrease in the corresponding coin's prices by 12 to 15 percent
• Coin prices do not recover to pre-attack levels one week after the event
• There are apparent positive abnormal returns generated by coins on the two days preceding a 51% attack
  • The researchers believe this suggests evidence of some insider trading or pump-and-dump schemes performed by the attackers prior to 51% attacks