CathInfo.com

The essencial and basics are Muslims worship "Allah" and his prophet muhammed. Catholics worship the trinity: the Father, the Son and the Holy Spirit all equally. Moslems reject the trinity. Moslems do not worship the same God as us, they worship a false man made created God. 

"Whoever denies the Son does not have the Father; whoever confesses the Son has the Father as well. " 1 John 2:23

This was always the true teaching of the church that the Muslims are heathens and infidels, only with the second vatican council and modernism which opened the doors for ecuмenism is that this is questioned by heretics.

Council of Florence, Cantate Domino (1441): "The most Holy Roman Church firmly believes, professes and preaches that none of those existing outside the Catholic Church, not only pagans, but also Jews and heretics and schismatics, can have a share in life eternal; but that they will go into the "eternal fire which was prepared for the devil and his angels" (Matthew 25:41), unless before death they are joined with Her; and that so important is the unity of this ecclesiastical body that only those remaining within this unity can profit by the sacraments of the Church unto salvation, and they alone can receive an eternal recompense for their fasts, their almsgivings, their other works of Christian piety and the duties of a Christian soldier. No one, let his almsgiving be as great as it may, no one, even if he pour out his blood for the Name of Christ, can be saved, unless he remain within the bosom and the unity of the Catholic Church." The same council also ruled that those who die in original sin, but without mortal sin, will also find punishment in hell, but unequally: "But the souls of those who depart this life in actual mortal sin, or in original sin alone, go down straightaway to hell to be punished, but with unequal pains."