I have a limited upstream bandwidth, and a single user was stealing all of it.
Download accelerators are EVIL, they download a single file in
multiple simultaneous connections, pulling their bandwidth, and
yours, to the max.
Some users hit pause/resume (or cancel/resume) constantly.
So if the accelerator uses 10 simultaneous connections,
each cancel/resume will hit your webserver 10 times.
making your logfiles grow a lot more than usual.
(in my particular case, I've found 89 requests from a single
user downloading a 5mb file with DA 5.0)
So, this is why I wrote this access rule. :)