A small botnet with an approximately 8600 zombie machines suddenly exploded and began to grow very quickly. At first it had been growing by 5-10 new computers per day. Today the botnet grew by 4400 new zombies! The average growth rate was about 1 zombie per second! Probably the owners of this botnet did a mass mailing of links to infected pages. Users must be very attentive while checking new emails: do not open messages from unknown senders, use only plain-text view of messages.”]
Source: https://securelist.com/a-look-inside-a-botnet/30361/