[rocqua]

A while ago bitcoin clients changed from facoring the 'longest' chain to favoring the chain with the most work done on it. (To prevent long chains with low difficulty)

[somebodythere]

So... the consensus rules of the network changed, you need to make sure you have the correct client, and bitcoin is weakly subjective after all?

[madacol]

Asking "what's the correct client?" will always be a subjective question

Bitcoin doesn't decide what is called bitcoin, we as a community do

[rocqua]

In practice this was essentially a soft-fork. But yes the consensus rules of bitcoin software changed.

[PeterisP]

The client can choose properly, but it needs to "call a friend" in order to get the options - if the client doesn't receive the proper chain but only fake ones, it will chose the fake one with the most work done on it.