Találtam egy ilyet a php.net-en, ötletes... :)

stephan@netlink.on.ca
28-Aug-2000 09:28

sleep() is useful as a hack delay. For example, in a login screen. Use
sleep() when you have determined the username/password combination entered
in a form is invalid. A sleep of a second is almost not noticable to the
user, but frustrates a cracker trying to use brute force methods to gain
access to your restricted area. Make sure you use sleep() before
outputting any HTML, otherwise you may tip the cracker that the login
failed before you enter sleep().