During and after lightning strikes, highly mobile cloud charge centers redistribute themselves attempting to find equilibrium with fixed earth charges including man-made conductive structures. This ACR creates electromagnetic fields similar to those of lightning. Differing rates of charge are a function of the buildings' various metallic systems. Charge differentials can occur due to faster buildup or reduction in one part than in another. When the dielectric breakdown of the air between the two sources is exceeded, a localized arc can occur.
Damage can range from data corruption to physical equipment failure.
Yet there may have been no observed lightning.