GameOver Zeus

Definition
GameOver Zeus is

"an extremely sophisticated type of malware designed specifically to steal banking and other credentials from the computers it infects. It's predominately spread through spam e-mail or phishing messages."

Overview
Unbeknownst to their rightful owners, the infected computers become part of a global network of compromised computers known as a botnet &mdash; a powerful online tool that cyber criminals can use for their own nefarious purposes. In the case of GameOver Zeus, its primary purpose is to capture banking credentials from infected computers, then use those credentials to initiate or re-direct wire transfers to accounts overseas that are controlled by the criminals. Losses attributable to GameOver Zeus are estimated to be more than $100 million.

Unlike earlier Zeus variants, GameOver has a decentralized, peer-to-peer command and control infrastructure rather than centralized points of origin, which means that instructions to the infected computers can come from any of the infected computers, making a takedown of the botnet more difficult. But not impossible.

Source

 * "Overview" section: FBI, GameOver Zeus Botnet Disrupted: Collaborative Effort Among International Partners (June 2, 2014) (full-text).