Why do people especially foreigners lookat nigerians so dubiously?

Iam asking this question because we have a variety of people from ediferent caste and creed and iwant to hear from the horses mouth . As a foreigner why are you always afraid of Nigerians or why do you always view them as thieves . i will actually welcome any good or bad experiences anyone has ever had with a Nigerian . Iam concerned with the bad image we being portrayed with . Since i consider Nigerian as one of the most hospitable and peaceful country Africa has to offer.