As of 2025, the full Intelligent Updater for SEP 14.x is approximately 350 MB for 64-bit Windows. It grows by roughly 15–20 MB per month.
Before and after a manual update, verify the date using PowerShell: symantec endpoint protection virus definitions download
It is worth noting the distinction between the scan engine and the definitions. The engine is the machinery that performs the scan, while the definitions are the data the engine uses. While engine updates (which fix bugs or improve heuristic analysis) are important, definition updates are released much more frequently—often multiple times a day. This is why the process is usually the most frequent maintenance task for IT teams. As of 2025, the full Intelligent Updater for SEP 14