Windows reserves many possible filenames as reserved 
device names.

Examples are prn.xxx, con.xxx, com1.xxx aux.xxx, etc, 
where xxx can be any extension.  Attempts to 
create/read/write to these files can hang the 
interpreter, but ideally would just throw an OSError.

A partial list of device names is mentioned at:
http://cert.uni-
stuttgart.de/archive/bugtraq/2001/07/msg00086.html