A mechanism for controlling the saving of an instant messaging session transcript to a log file. The system includes a session locking feature that allows a participant (e.g. the session initiator) to lock the entire contents of a session transcript saved into a log file. The system further includes a message locking features that allows a participant to selectively lock a specified portion the contents of the session transcript saved to a log file. The locking participant is able to indicate which other participants can unlock the content in the session transcript stored in the log file that they have locked, and those specified other participants are accordingly sent the necessary key to unlock such locked content. The system further allows users to subsequently request locks to unlock content in a session transcript stored in a log file, and for the locking participant to selectively allow or disallow such requests.