The number of reachable nodes has declined further following an ‘attack’ that overloaded the bitcoin network. Last week, an unknown actor sent a deluge of spam that left bitcoin’s nodes with upwards of 88,000, or 1GB worth, waiting in their collective memory pool. Core developer Jeff Garzik implemented a ‘quick fix’ for operators, but the number of nodes is now 16% lower than before the attack. The memory pool has returned to normal (around 4MB at press time) despite the memory pool returning to normal.”]
Source: https://www.coindesk.com/markets/2015/10/15/bitcoin-node-numbers-fall-after-spam-transaction-attack/