At present, one of the main methods of minimizing risk resulting from electromagnetic information leakage is to attenuate the undesired levels of radiated and conducted disturbances generated by IT equipment, as these disturbances can carry information processed by said equipment. Attenuation of conducted compromising emissions is most commonly handled with filters with a sufficiently high insertion loss. This article defines an original analytical relation specifying insertion loss value requirements for mains filters and estimates values of parameters included in the defined relation. Furthermore, this defined relation was used to define requirements for insertion loss provided by the mains filters, above which the ratio value of potentially compromising conducted emission levels to the environmental noise level at the infiltrating system input S/N < 0 dB. As a consequence, electromagnetic infiltration is significantly impeded.