TIES selected the string +++ATvalid command<cr> as its escape sequence, the shortest valid command being simply +++AT<cr>. This relied on any file describing such a system to be unlikely to place the command on a line followed immediately by a carriage return. Nevertheless, this was going to occur at some point, and more annoying, could happen at random in a binary file, like a .zip. This would occur, on average, about once per gigabyte, which was at that time an extremely large size – most hard drives of the era were about 40 MB. Hayes estimated that a user transmitting files for one hour a day would encounter about six files per year that randomly contained this sequence and drop the modem into command mode. For the average user, this would be mysterious.