  We briefly review contemporary extragalactic {\gamma}-ray propagation models.
It is shown that the Extragalactic Magnetic Field (EGMF) strength and structure
are poorly known. Strict lower limits on the EGMF strength in voids are of
order 10^{-17}--10^{-20} G, thus allowing a substantial contribution of a
secondary component generated by electromagnetic cascades to the observable
spectrum. We show that this "electromagnetic cascade model" is supported by
data from imaging Cherenkov telescopes and the Fermi LAT detector.
