This button is activated if there is a file called sqlnet.ora in the location defined in TNS_ADMIN system variable. If you want to disable this button, just remove or rename the file.
Toad for Oracle is checking the TNS_ADMIN path. If you go to Environment variables (Right-click on My Computer | Properties | Advanced System Settings | Advanced tab | Environment Variables...), you will find a variable TNS_ADMIN with a system path. The sqlnet.ora can be found there.
