Genesis 42:9

Ye are spies. The “hard things” Joseph spoke to his brothers are now revealed. Egypt had always been suspicious of its eastern neighbors, who had not only raided Egypt and then vanished back into their desert abodes, but had in the past infiltrated Egypt and actually taken over the government of parts of the country. Such incursions during the First Intermediate Period, prior to the Twelfth Dynasty, had led King Amenemhet I to build border fortifications between the Mediterranean and the Red Sea, called “Wall of the Ruler,” to keep the Canaanites out of Egypt. The Hyksos, coming afterward and also from the east, had now gained the supremacy of the country and were watchful that others might not do to them what they had done to the Egyptians. It was therefore natural for Joseph to examine all easterners carefully, and make an effort to detect any undesirables or actual spies. Since the famine raging in the neighboring countries brought great numbers of foreigners to Egypt as grain purchasers, greater care had to be taken to weed out those whose presence in the country might endanger its security.