Unless under a court order, given written permission to do otherwise, or impending potential harm to a client or others, everything discussed between a coach and client will remain private and confidential. However, a coaching relationship is not afforded the same status as a doctor-patient relationship by the courts, and a court may, in some circumstances, be able to force my coach to testify.
Although a coach will never disclose information acquired through any means other than court order and/or potential harm to others, I also understand digital communications may be intercepted by others if they are not protected by encryption (and sometimes even if they are) and/or are stored on computers connected to the internet. I know this is especially true for email, but may extend to other communications technologies.
If participating in group coaching of any sort each member will sign an agreement to maintain the confidentiality of fellow group members by never disclosing details which would allow the recipient to identify the group member to whom these details pertain.