Automatic shutdown of infected network connections

Some universities such as Vanderbilt University are automatically shutting down network ports when they detected signature worm traffic. Almost 25% of the students' computers were detected as infected when they connected to the university network. http://www.vanderbilthustler.com/vnews/display.v/ART/2003/08/29/3f4eb4b3537e... How many ISPs disconnect infected computers from the network? Do you leave them connected because they are paying customers, and how else could they download the patch from microsoft?