Magnetic field disturbance accompanying dust particle impacts is explained by means of the creation of a secondary cloud around the Giotto spacecraft. The enhancement of the magnetic field is seen as a result of the deceleration of electrons in the cometary plasma flow due to collisions with neutral atoms of the cloud surrounding the spacecraft. As the magnetic field lines are frozen into the electron component of the plasma flow, this deceleration leads to an increase of the magnetic field strength. The electric current responsible for the magnetic perturbation is the electron drift current under the action of the friction force between electrons and neutral atoms. Impact-produced cloud parameters were estimated by using the magnetic disturbance and the angular distribution of the scattered cometary ions. ¿ American Geophysical Union 1995