Re: 64. Can the Transfer of the Inventor of the Puzzle Be Manipulated?
Yeah probably possible. On the other hand, why would you listen for potentially few years on the nodes with ready to crack hardware to get 1.2 btc to make a potentially successful double spent attack?
1.2 BTC is currently worth close to $75k. Someone could potentially create a program that listens for a transaction that spends one of a set of outputs, rents a VPS and GPUs on GCS, and executes a script that will find the private key, and create a competing transaction.
Where did this value of 1.2 BTC come from? 
The Puzzle #64 address only has a balance of 0.64020585 BTC
Or is the 1.2 BTC the total value of all the "prizes" that have been claimed so far... and someone is theorising that an attacker may have attempted to setup a monitoring rig to try and steal all the prizes?