Well, I would say on the whole very little and at best not at all. However, like a lot of cranks, he has a small public, which is not likely to increase very much, when his untruths are further exposed by real historians. The last I heard of him, he was in prison for Holocaust denial in Austria. You may or may not agree with the laws of Austria. At any rate, that alone should give you some idea of how he earned his notoriety.