In the ranks of digital bank robbers, these crooks stand out as smooth operators. The Carbanak cybergang made off with as much as $1 billion from 100 financial institutions worldwide—without raising the usual alarm bells. Patient and coolly methodical, this international crime ring slips covert surveillance programs into a bank’s internal systems, so it can spy on staff to learn how to make fraudulent transactions look legitimate. Kaspersky experts worked with law enforcement to track the operation, uncover how the heists went down, and identify the warning signs that a bank’s network is under siege.

Infographic: Banks Face Massive Losses From Carbanak Attacks