A worm detection module (WDM) (212) stops worms and other malicious software from spreading among computer systems (100) on a network (210) via open drive shares. The WDM (212) monitors (310) a storage device (108) for activity (314, 316) directed to executable files by remote processes. The WDM (212) flags (318) files (216) that are the target of such activity. If a flagged file (216) attempts to create an executable file (218) on a networked computer system (100B), the WDM (212) detects (322) that the flagged file (216) is a worm. In response, the WDM (212) blocks the write to the networked computer system (100B) and thereby prevents the worm from propagating.