A User that has no need to edit the TNSnames.ora file has the ability to. Would like disable users from having this ability.
1. Select the directory where tnsnames resides (Toad will tell you where this is).
2. Highlight the tnsnames file, then right-click and select Properties.
3. Under the Security tab | Advanced options, the SYS Admins can make the file read-only. When the file is read-only, a lock will appear next to the tnsnames editor button in Toad.