Computers store everything as electric current. If the current is on it's a one. If the current is off it's a zero. High energy particles from outer space regularly blast through our upper atmosphere into the Earth passing through most solid matter. These high energy particles can induce the electric currents when they impact computer components. These erant current can cause a one to become a zero or a zero to become a one. This can have all kinds of interesting effects depending on which zero and one got changed when and where. Normally this causes a crash of the program or operating system.