some times you may want to disable right click on some certain parts of your website for reasons best known to you probably to not let people view your source code. Here is how to do it using jquery http://www.pwlabs.com.ng/2014/09/how-to-disable-right-click-using-jquery.html

well it is very easy to undo that, just save the page and remove the line that imports jquery to the webpage and voila!

For php sites your best bet is to use a plugin.

I have to point out that no matter how hard you try to obscure your source code, anyone who is smart enough to use Telnet can get it anyway, unless you disable it. i am fairly sure about how you disable it on a linux server:

# grep /etc/xinetd.d/telnet disable=no

#nano /etc/xinetd.d/telnet

and change disable=no to disable=yes. idk how to do it on a windows server ^.^