The invention relates to the selective protection of blocks of text (118, 122, 128) or other portions (123, 125, 126, 127) of a shared data object in collaborative computer based system from simultaneous manipulation by two or more users. The collaborative computer based system includes a network connecting a plurality of terminals for communication. Each terminal includes an output display device and a user input device. The collaborative computer based system includes a shared data object (117) simultaneously accessible by a plurality of users of the system. Responsive to a user obtaining access to the shared data object, the user is assigned a cursor (138) available for display on the visual display devices of all current users. A user may attempt to protect portions of the shared data object with a lock region (136) by selecting position coordinates for such a lock region. If the position coordinates do not include any portion of any previously established lock region, a lock region is established, blocking manipulation of the portion of the shared data object so covered against changes associated with cursors other than that of the establishing user. Exercise of appropriate commands release any prior lock region associated with the user.