Word for person unwilling to share information [closed]

One possibility is to use:

reticent (n.): not willing to provide information about something, especially about yourself or your feelings.

In addition to Mehper's answer, I'd suggest discreet might be a good word, if you mean this in the approving sense, or close (meaning 18: Secretive; reticent: "was close about her personal life" ) otherwise. Secretive might also apply in extreme cases.

I would use secretive.

Secretive: inclined to secrecy or reticence about divulging information.

I would submit: Paranoid.

Use with caution.

If it is about private information, the person could be said to be privacy aware.