Last year I used the following method: skype is a program which does not
send a "User-Agent:" header to the HTTP proxy (squid).
This is not considered a good practice in RFC2616:
http://tools.ietf.org/html/rfc2616#section-14.43
So I added to squid.conf the following two lines:
acl validUserAgent browser \S+
http_access deny !validUserAgent
(this second line must be place/order in the right place on your
http_access list of squid.conf)
And skype stopped to work (1 year ago... now, really, I'm not sure if it
still working).
Giovanni
