Mystery and danger loom over major U.S. retailers and grocery stores, including Walmart, Kroger, Meijer, and Whole Foods, who have been targeted by an unsettling series of hoax bomb threats. What Happened: The Wall Street Journal reported that the calls demand thousands of dollars in gift cards, Bitcoin (CRYPTO: BTC) and cash, with the ominous threat of detonating bombs if the demands aren’t met.