What is sad.. is the number of people who tie them selves in knots trying to figure out clever ways to attack bitcoin using 51% attacks and other 'clever shit' and working out all the cost that it would entail
.
In reality it only requires an attack on the software.
All that money trapped by the FBI
it's only trapped because that is the way the software is written.
The hard part isn't changing the software.
The hard part is convincing every single node on the network to run your changed software instead of the original software.