Secure & Insecure Services

In all honesty anything you dont need.
When setting up a firewall it is best to close all ports and then open only the ports that you or the others on your network need.

Also you may want to look into getting rid of telnet and going with OpenSSH(http://www.openssh.org) this will make a secure connection when you have to remotly administrate your system. This is much better than telnet which doesnt encrypt anything and allows those evil oones out there to free read your packets and intercept valuble information such as passwords...

In general a secure service when talking about protocols can be considered one that has built-in application level security. For example, ftp prompts you for a login and password. Http is not secure because it is anonymous. Good firewalls allow out of band authentication which allows you prompt for login and password on protocols such as http. If you are asking about services as in NT services, then an insecure service is any one that the firewall doesn't need to function. Such as the "at" service which someone can use to activate a trojan.

If you aren't getting the answers you want, please try to be more specific. We don't have much room to answer.

One of the problems here is that secure & insecure can mean a lot of different things to different people. While telnet & FTP services can require passwords to initiate a session, the information transmitted accross those connections is readable byanyone that might happen to be looking(ie. hackers), this includes the password used to log in. to me this is insecure. A secure service would encrypt the data transmitted between the two computers so that only those two computers can read it. Examples of secure services would be like SSL used in e-commerce and VPN services. Several commercial firewalls have VPN services built in or available as plug in's, that makes setting up a VPN fairly painless.

Hope this helps