I Love You
Discovered in 2000, the "I love you" or "Love Letter" malware was not the first example of using social engineering to infect computers, but it was the first massively successful one," says Haley.
Subsequently, it provided a foundation for cyber social engineering that still works today: everyone wants to know that someone loves them. On the flip side, it also taught computer users that they can't trust everything they see online or receive in their inbox. (Though that lesson clearly hasn't settled in fully.)