Sources are by default "Public", they can be seen by all the users on the platform. You can make a particularly sensitive Source "Private".
Step 1:
If it's an existing source, go to the 'Sources' section, choose a source and click on the 'Settings' tab. Otherwise Start creating a new Source.
Step 2:
Check the "Private Source" box and click on "Edit"
Step 3:
Now you are the only person able to see and follow this Source.