[maxerickson]

Miners could conspire to mostly freeze certain bitcoin.

It wouldn't even have to be done in a way that was visible on the bitcoin network, they would just have to agree to not include transactions from whatever addresses.

A strong majority could probably refuse to acknowledge blocks including the blocked addresses, which would be a real freeze (rather than the hassle freeze obtained by not including the address in blocks produced by the conspiracy).

[jsprogrammer]

You'd need >50% of the miners to do that. It is precisely what I mean by building a protocol.

Of course, without strong consensus (and a real algorithm/protocol) such attempts will likely just result in fractured blockchains (basically the state at the moment, with many competing implementations of the same basic idea).

[csomar]

Not really. you are talking about an attack.

You'll need 100%, because if a single miner decided to include the transaction, then it is in!

[maaku]

You need only a cabal of >50% of the miners to agree to not build on any block that includes such a transaction.

[jsprogrammer]

An attack and a new protocol are the same thing.

If a single miner includes the transaction, a majority can just bypass that sole miner.

You do need 100% of something, but that something is just >50% of the miners.

[bduerst]

Only if that miner is successful for a block. Until then the blocked transaction stays in limbo.