Abstract: A mosaic printer is made secure from unauthorized interception of data by falsifying the needle drive pulse current magnitude and sequence so that electromagnetic leakage radiation cannot be used to determine the alphanumeric data being printed. This falsification is accomplished by a compensation device having compensators energized each print cycle in addition to the printer needle drives in a reciprocal or a pseudorandom manner. The compensators have current consumption characteristics nominally identical to the needle drives and produce substantially identical radiation pulses, making it impossible to correlate the radiated pulse format with the symbol being printed.