Obviously the Moslems are taking revenge for the pillaging of their homelands by the Vikings. Thus these are merely reparations that the Moslems are owed by the modern day descendants of those 9th-12th century Vikings.
Surprisingly, the Vikings did attack Moslems in North Africa and in Persia.
And the earlier Crusades and fighting in S. Italy, Cyprus and Sicily were dominated by Normans, a few generations descended from Vikings.