The earth's own magnetic field is usually strong enough to deflect and absorb most of the radiation put out by the Sun. Occasionally the sun will form an open field line region on its surface, creating a coronal hole and generating a high-speed solar wind stream. This stream interacts with the ambient solar wind, increasing the bow-shock to the earth. These disruptions in the Earth's magnetic field can cause it to stretch and break at the poles, either reconnecting the lines to the interplanetary magnetic field, (field produced by the sun and other heavenly bodies in the solar system), or dragging them back into the tail region. Regardless, there is now a hole in the magnetosphere, allowing the solar wind to directly interact with the atmosphere at those points, producing magnetospheric substorms and a ring current.
     For the solar wind to create a geomagnetic storm large enough to have a significant impact on the performance of electronic devices, a significant increase in radiation is necessary. This will be most probable in a period of high solar wind and frequent solar flares, called a Solar Maximum Event. For a period of about a month every eleven years, the solar wind can radiate nearly 100 times as much matter than average, producing much stronger magnetic fields and exciting the earth's magnetic field and atmosphere. Combined with a coronal mass ejections which could disturb the solar field as well as reduce the cover of the earth's magnetosphere, the magnetic field disruptions could be as high as 1T.
     According to research by TSU at the National High Magnetic Field Laboratory, significant impairment of operation for MOSFET type transistors occurs at 4T and above. While a 1T magnetic storm may not directly cripple any transistors, it would certainly do damage to those already in the presence of magnetic fields, such as those on computer hard drives containing magnets and perhaps power control systems exposed to high voltage.
     When the ring current forms under conditions such as these, it too can play an influential role in disrupting electronics. The ring current, though fairly high in the atmosphere, causes mutual inductance in electronic systems on the ground. Take a DC system running in the opposite direction of the ring current for example; it will gain an amount of current proportional to the ring current, potentially burning out the system. A DC system running in the same direction will lose current, shutting down the system.
     The third effect that a massive geomagnetic storm could produce is an induction of current in civil projects that were never meant to carry significant current, such as oil and gas pipelines and telecommunications cables. Like with the hypothetical DC system, a current will be induced in the line traveling in the opposite direction of the ring current. This could be very costly if the line is not grounded correctly, as a high voltage discharge could damage the line itself and anything, living or not, which happens to ground it.