Computer implement methods, apparati, and computer-readable media for enabling a first computer (12) to determine that it is safe to communicate with a second computer (10) coupled to the first computer (12) over a network (15). In a method embodiment of the present invention, the first computer (12) detects (21) that the second computer (10) has initiated a test open of a file (14) associated with the first computer (12). When the test open is followed by an actual open command by which the second computer (10) seeks to actually open the same file (14), the first computer (12) determines (23) that it is safe to communicate with the second computer (10).