A method and system prevents data stored in a computer system from being manipulated, particularly via hacker attacks and virus infection. The system allows multiple access by including means for assigning at least one of the in the assigned set of identification codes to more than one mobile telephone. A first magnet and a second magnet are connected to the shaft and rotatable around the axis of rotation in response to rotation of the shaft. If the change made to the corresponding node in the second data structure does not create a collision with the first data structure, then the change is made to the accessed node in the first data structure.