Swine flu is caused by any strain of influenza endemic in pigs. The 2009 outbreak was a new H1N1 strain derived from human, avian, and pig influenza viruses. As the outbreak spread globally, countries and citizens took steps to protect themselves through masks, cancelling trips, and avoiding crowds. The WHO raised its alert level to Phase 5, indicating a pandemic was imminent, as the virus spread rapidly globally. Prevention measures include avoiding affected areas, caution around travelers, frequent handwashing, covering coughs and sneezes, and wearing masks. The key is prevention through awareness, not panic.