Public Data vs Private Data in Trello
We don't want you to get a surprise that you've shared something you intended to keep private. You have full control over the visibility of your data, and all defaults favor privacy.
You have the ability to make boards and organizations private, in which case only added members will be able to view the board or organization. Actions on private boards and organizations will not show up in profiles. Private organizations and boards are not visible in search.
Your member profile is public. That includes your full name, username and bio, not your email. (If you set your full name to be your email, people will see that.)
Other users will only see actions on your public boards (unless they are part of one of your private boards or organizations). Boards pages will list only public boards and organizations.
See also Security, Backup, & Data.