Carbanak
A criminal group and its backdoor that, from 2013, broke into about a hundred banks and emptied them by behaving exactly like the banks' own staff.
Kaspersky published its report in February 2015 and put the haul at up to a billion dollars from banks in some thirty countries. The way in was mundane: emails with attachments sent to bank employees. Once inside, the group recorded screens and keystrokes for weeks to learn how staff actually worked, then used the bank's own systems against it.
The cash-outs were well thought through. A balance might be raised from 1,000 to 10,000 dollars and the difference moved out, leaving the account holder none the wiser. Cash machines were told to dispense notes at a set time, where a mule happened to be waiting. The alleged leader was arrested in Spain in 2018, but the code lived on and is associated with the FIN7 group.