Dropper An executable file that, when run, "drops" a virus. A dropper file has the capability to create or run a virus and infect the user's system when it is executed. When a dropper file is scanned, the scan may not detect a true virus, because the viral code has not yet been created. The viral code (and virus) is created when the dropper file is executed. Heuristics scanning often detects droppers before regular scanner.