Today, a federal appeals court struck down a 2008 Indiana law that banned registered sex offenders from using social media sites such as Twitter and Facebook.

The challenge was brought by an anonymous Hoosier who is on the state's sex offender registry as a result of a 2000 conviction for child exploitation. When the Indiana legislature passed a law banning him from using social media sites, he brought a legal challenge arguing the law violated his First Amendment rights. A lower court judge rejected his argument. But on Wednesday, the United States Court of Appeals for the Seventh Circuit overruled his decision.

"Illicit communication comprises a minuscule subset of the universe of social network activity," wrote a unanimous three-judge panel. "As such, the Indiana law targets substantially more activity than the evil it seeks to redress."

That's a problem because under Supreme Court precedents, regulations that target speech must be "narrowly tailored" to achieve a significant government interest. While deterring sexual exploitation of minors is obviously a legitimate government interest, the court found a total ban on accessing social media sites was too broad to pass muster.

The Seventh Circuit's ruling could influence pending litigation in San Francisco over a California initiative that requires sex offenders to provide the government with a list of their social media identifiers. Earlier this month, a federal judge issued a preliminary injunction against the law. While decisions of the Seventh Circuit are not binding in California courts, Wednesday's ruling is likely to be cited in future litigation over the California measure.