INDIANAPOLIS — A new state law that would have allowed the computers of sex offenders to be searched long after their sentences had been served violates their constitutional privacy rights, a federal judge ruled Tuesday.

Starting July 1, the law would require sex offenders enrolling in the state’s public registry to submit e-mail addresses and user names for instant messaging, chat rooms and social networking sites.

Those who provide that information would have to sign a consent form allowing searches of their computers or other Internet-enabled devices at any time. They would also have to install software that monitors their Internet activity at their expense.

Failure to consent to those measures would be a felony.

The restrictions already were conditions of probation, but the American Civil Liberties Union challenged their use on privacy grounds for sex offenders who must still register but have finished serving parole or probation.

U.S. District Judge David Hamilton agreed with their claims.

“The unprecedented new law, however well-intentioned, violates the Fourth Amendment rights of the plaintiff class, who have completed their sentences and are no longer on probation, parole or any other kind of court supervision,” Hamilton wrote in a 51-page ruling.

“The state may not force them to waive those rights under threat of criminal prosecution for failing or refusing to do so,” the ruling said.

In defending the lawsuit, the state argued among other things that sex crimes were a serious threat in the U.S. and there was a “special need” to conduct suspicionless searches of sex offenders’ Internet-capable computers and telephones at any time to protect the public.

The state attorney general’s office was reviewing the ruling and had no immediate comment, said spokeswoman Staci Schneider.

Sex offenders generally must be actively registered for 10 years after their release from prison, but some face the restriction for life.

State Sen. John Waterman, R-Shelburn, sponsored the bill that ultimately included the new computer search language. The bill originally had nothing to do with sex offenders.

But late in the session, a conference committee inserted several provisions — including the ones dealing with computers — that Waterman said he supported.

A message seeking comment was left at Waterman’s home on Tuesday.

He said when the lawsuit was filed last April that the law was another way to protect children from sexual predators, in this case those who seek out victims through the Internet.