Program Download Technique is a high-level term for the suite of vendor-specific API calls used to configure a controllers user program memory space. The granularity of control to transfer a user program in whole or parts is dictated by the management protocol (e.g., S7CommPlus, TriStation) and underlying controller API. Adversaries may choose to avoid a download all in favor of an online edit or program append to avoid disrupting the physical process. Stuxnet’s infection sequence consists of code blocks and data blocks.”]
Source: https://collaborate.mitre.org/attackics/index.php/Technique/T0843