Two months before Zeran's suit, Congress had enacted the Communications Decency Act of 1996, a mostly anti-porn law that the Supreme Court would later strike down on First Amendment grounds. The law contained something else, though: a provision now best known as Section 230. //

But just how sweeping was this law?

Before Zeran, it was hard to say. The 26 words of Section 230 that give "interactive computer services" immunity were inscrutable. Debate raged about how broad or narrow the words should be seen.

But when the U.S. Court of Appeals for the 4th Circuit issued its opinion in Zeran's case, it strongly favored AOL, expanding and strengthening the law and leaving little doubt about just how powerful this legal shield is.

"Congress recognized the threat that tort-based lawsuits pose to freedom of speech in the new and burgeoning Internet medium," the court wrote. "The imposition of tort liability on service providers for the communications of others represented, [is] for Congress, simply another form of intrusive government regulation of speech."

With that ruling, tech companies no longer had to fear getting sued for something users posted, even if the online service was put on notice about defamatory content. It helped propel tech startups into multi-trillion-dollar global behemoths. Scholars call the Zeran decision "the most important Internet law ruling ever."