July 2015 flood attack

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

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, leaving sites including Blockchain.info and TradeBlock temporarily impaired.

Peter Todd may be a major contributor, as evidenced by a discussion involving him on /r/Buttcoin, in which he offers to execute a stress test for $5,000. It has also been speculated that the attack is the product of mining pools in an attempt to drive up transaction fees.^{[citation needed]}