Fees spiked to around $2 just before a difficulty adjustment, unexpectedly sending transactions out of the queue as new ones were made with far higher fees, thus gaining priority for the very limited 1MB (~2,000 transactions) space.
What exactly caused this sudden spike is unclear. With a number of potential reasons suggested by the two bitcoin camps.
Some say many transactions were suddenly performed by one entity, but with bitcoin being what it is, that can only be a guess.
They call it spam, by which presumably they mean the transactions were not intended to transfer value, but for something else.
They propose two contenders for performing this very expensive spam operation which costs some $50,000 to $100,000. Their political opponents, the big blockers, presumably to score some cheap points, or perhaps more realistically, the miners.
A $100,000 investment, which miners don’t even have to pay, to increase transaction fees to $5 or so, thus around $10,000 per block or $60,000 per hour, sounds, in many ways, like an obvious choice.
Especially if it is done with the assistance, or even encouragement, of some developers, who clamor for higher fees to put in place their settlement system.
But in the bigger picture, today’s spike seems minuscule, even though fees have considerably increased as stated earlier.
As such, it may well be the case that rather than one entity, the congestion increased because, firstly it is Monday and the start of a new working day, and secondly, as well as more importantly, because mining difficulty increased by 20%.
Technically, if no new hashrate is added to the network, then blocks would be found more slowly. With the network already near limits, the slow down in processing speed may have instantly created that spike, followed by the increase in fees.
This unpredictability and very sudden network processing speed adjustment may make the maintenance of a fee market difficult if at all possible, with increases and decreases being cyclic.
As such, if this was an attack or otherwise, it may well be the case that both sides can agree it is a vulnerability for the network which is currently operating at full capacity.