In early June, 2016, the Russian police arrested the alleged members of the criminal group known as Lurk. The police suspected Lurk of stealing nearly three billion rubles, using malicious software to systematically withdraw large sums of money from the accounts of commercial organizations, including banks. For Kaspersky Lab, these arrests marked the culmination of a six-year investigation by the company’s Computer Incidents Investigation team. We are pleased that the police authorities were able to put the wealth of information we accumulated to good use: to detain suspects and, most importantly, to put an end to the theft. We ourselves gained more knowledge from this investigation than from any other. This article is an attempt to share this experience with other experts, particularly the IT security specialists in companies and financial institutions that increasingly find themselves the targets of cyber-attacks.