A federal judge late Friday blocked enforcement of a California voter-approved measure that would have dramatically curtailed the online, First Amendment rights of registered sex offenders.

Proposition 35, which passed with 81 percent of the vote in November, would have required anyone who is a registered sex offender – including people with misdemeanor offenses such as indecent exposure and whose offenses were not related to activity on the internet – to turn over to law enforcement a list of all identifiers they use online as well as a list of service providers they use.

U.S. District Judge Thelton Henderson of San Francisco also said the measure was overbroad.

"The challenged provisions have some nexus with the government's legitimate purpose of combating online sex offenses and human trafficking, but the government may not regulate expression in such a manner that a substantial portion of the burden on speech does not serve to advance its goals," he wrote.

The Californians Against Sexual Exploitation Act would also have forced sex offenders to fork over to law enforcement their e-mail addresses, user and screen names, or any other identifier they used for instant messaging, for social networking sites or online forums and in internet chat rooms.

The American Civil Liberties Union and the Electronic Frontier Foundation immediately filed suit after its passage. The measure would currently affect some 75,000 sex offenders registered in California, but the law also requires those convicted of human trafficking to register as sex offenders, thus widening the pool of people affected.

The measure carries three-year prison penalties.

Henderson had tentatively blocked enforcement of the measure immediately after it passed. His decision Friday is in the form of a preliminary injunction. Next up is a trial on the lawsuit's merits, if it gets that far.