July 2015 flood attack

The July 2015 flood attack is an ongoing "stress test" of the Bitcoin network. The possibly distributed attack has provoked hundreds of thousands of transactions, leaving over 80,000 in the mempool at one time. The attack is subsequent to stress tests executed in June.

Some single-word brainwallets ("password", "cat", etc.) have been the recipients of thousands of transactions, leaving 0.00001 BTC outputs. F2Pool has been concatenating these outputs in huge 1MB transactions. These transactions fill up an entire block on their own, and are far too large to be relayed by nodes; they have only been confirmed because F2Pool dedicated blocks to them. Some nodes report having spent over 20 seconds on one of these transactions, explaining momentary but extreme latency and downtime on block chain explorers.

Motivation

The attackers may have an agenda related to the blocksize debate, attempting to demonstrate the infeasibility of 1MB blocks including transactions of hundreds of thousands of users. Specifically, the Chinese mining pools (AntPool, BW Mining, F2Pool, BTC China, & Huobi) have expressed distaste towards Gavin Andresen's proposals to increase the blocksize limit, citing concerns of relatively low bandwidth compared to that available in the United States and Europe. The flood attack may be attempting to discredit the pools, and subsequently force them off the network after the raised blocksize limit is in effect.

It is unlikely that the attack is being used in an attempt to damage or shut down Bitcoin, as it appears to be controlled and benevolent.

Suspects

Coinwallet.eu, who had executed the previous stress tests, may have something to do with this attack as one of the bitcoin addresses has been used in both efforts. However, Coinwallet.eu did not announce involvement in this attack, as they had in the stress tests.

Peter Todd had previously offered to execute a stress test for $7,000 but he denies involvement in this attack.

Redditor /u/TheGiv3r has published the private keys to hundreds of addresses which have been recipients of dust outputs in 2013, perhaps in an attempt to incite additional spam as redditors try to claim the funds.

Satoshi Nakamoto has been (perhaps jokingly) labelled a suspect, as he had mentioned that the block size should be increased when it is needed and may be campaigning for this change without revealing his involvement.