How to Block skype on squid proxy server

Edit squid.conf and add the below mentioned lines. This will allow skype for user1, user 2 and deny for all.

acl numeric_IPs url_regex -i ^([0-9]+\.[0-9]+\.[0-9]+\.[0-9]+)

acl Skype_UA browser ^skype^
acl Skype_Allowed_Users proxy_auth user1 user2

http_access deny numeric_IPS !Skype_Allowed_Users
http_access deny Skype_UA !Skype_Allowed_Users 


http_access allow ntlm_users
http_access deny all