Task menu reference
Task|Hide tasks
The Hide tasks command sets the other users who are also allowed to open the current markbook. Only the owner of the markbook can use this command. Select the name of a task in the Visible tasks list, and click on the Hide button to move the task to the Hidden tasks list. Repeat this for all tasks who you want to hide. To remove a task from the Hidden tasks list, click on the name and then the Remove button.
Click on the Save Changes button when the list is complete.
Hidden tasks are available in all commands in SM-Marks Online and take part in calculations, but are hidden from the main view. When opening a markbook with hidden tasks a message is shown to remind you that not all tasks are visible.