Earlier this summer, thousands of Americans received mysterious packages of seeds, postmarked in China, that they didn’t order—sparking a federal investigation. Now, Amazon has decided to ban foreign sales of seeds to U.S. customers as “part of our ongoing efforts to protect our customers,” The Wall Street Journal reported. “Moving forward, we are only permitting the sale of seeds by sellers who are based in the U.S,” a spokesperson told the newspaper. The U.S. Department of Agriculture, meanwhile, is still trying to figure out who sent the seeds and why—and whether they posed any kind of threat.