The American Civil Liberties Union of Indiana filed the class-action suit on behalf of a man who served three years for child exploitation, along with other sex offenders who are restricted by the ban even though they are no longer on probation. Federal judges have barred similar laws in Nebraska and Louisiana.
"We will be appealing," ACLU legal director Ken Falk said in an email Sunday to The Associated Press. Appeals from federal courts in Indiana go to the 7th U.S. Circuit Court of Appeals in Chicago.
Courts have long allowed states to place restrictions on convicted sex offenders who have completed their sentences, controlling where many live and work and requiring them to register with police. But the ACLU claimed that that Indiana's social networking ban was far broader, restricting a wide swath of constitutionally protected activities.
The ACLU contended that even though the 2008 law is only intended to protect children from online sexual predators, social media are virtually indispensable and the ban prevents sex offenders from using the websites for political, business and religious activities.
But Pratt found that the ban is limited only to social networking sites that allow access by children, and that such sites aren't the only forms of communication on the Internet.
"The Court readily concedes that social networking is a prominent feature of modern-day society; however, communication does not begin with a "Facebook wall post" and end with a "140-character Tweet," she wrote.
Though the law doesn't list which websites are banned, court filings have indicated the law covers Facebook, MySpace, Twitter, Google Plus, chat rooms and instant messaging services. Earlier filings indicated LinkedIn was also covered by the ban, but Pratt's ruling said it wasn't because children under 18 can't sign up for it.
"It is a very well-reasoned opinion and the Indiana statute has certainly attempted to be specific," said Ruthann Robson, a professor of constitutional law at the City University of New York. But she faulted the judge and the law for treating all sex offenders as if they were likely to commit another offense.
"A better statute might provide for some sort of individualized determination rather than a blanket prohibition," she said.
Social networking bans have been struck down in two other states.
In February, U.S. District Judge Brian Jackson found that Louisiana's prohibition was too broad and "unreasonably restricts many ordinary activities that have become important to everyday life."
Pratt said Indiana's ban wasn't as broad the overturned Louisiana ban.
Louisiana lawmakers passed a new law last month that more narrowly defines which sites are prohibited. News and government sites, email services and online shopping are excluded from the new rules, as are photo-sharing and instant messaging systems. The measure takes effect Aug. 1.
In Nebraska, a federal judge in 2009 blocked part of a law that included a social networking ban. A second legal challenge by an Omaha-area sex offender is set for trial in July.