WikiLeaks released documentation on another CIA cyberweapon. Codenamed Pandemic, this is a tool that targets computers with shared folders. Pandemic can replace up to 20 legitimate files at a time, with a maximum size of 800MB per file, and only takes 15 seconds to install. The tool was specifically developed to replace executable files, especially those hosted on enterprise networks via shared folders. The role of this cyberweapon is to infect corporate file sharing servers and deliver a malicious executable to other persons on the network.
Source: https://www.bleepingcomputer.com/news/security/cia-malware-can-switch-clean-files-with-malware-when-you-download-them-via-smb/