"What happens to you here is forever," warns O'Brien, an agent of the Thought Police, in "1984." He would've loved the internet.
Online, everything is forever. All the sites you visit, articles you like, posts you share: They're in the permanent file. Facebook Inc.'s most recent scandal -- in which it allowed an outside company to furtively collect its users' data on a huge scale -- caused an uproar in large part because the people affected thought they were taking a harmless and ephemeral quiz; instead, their answers were stored for years and used in ways they never expected.