Drew, an adult Missouri resident, was prosecuted for allegedly violating a federal computer fraud law by helping to hatch a plan to create a fake profile of a boy, "Josh," who sent messages to the teen. While the messages were initially flirtatious, they eventually became hurtful. The teen hanged herself after receiving a final message from "Josh" that the world would be a better place without her. Drew herself didn't send the messages or create the account, according to the trial testimony.

Authorities in Los Angeles charged Drew with committing computer fraud on the theory that she violated MySpace's terms of service by helping to create the profile. Last year, a jury convicted Drew of three misdemeanor counts of computer fraud.

Wu said in July that he was going to set aside that ruling. In his written decision, he said that a criminal prosecution for violating a site's terms of service violation "runs afoul of the void-for-vagueness doctrine."

Among other reasons, Wu held that such a prosecution is invalid because defendants don't have fair notice that ignoring or violating a user agreement can result in criminal sanctions.

He also pointed out that MySpace's terms of service are so broad that many people apparently violate them. For instance, he wrote, "the lonely-heart who submits intentionally inaccurate data about his or her age, height and/or physical appearance" violates the site's prohibition against providing false or misleading information. In addition, "the exasperated parent who sends out a group message to neighborhood friends entreating them to purchase his or her daughter's girl scout cookies" breaks the site's rule against advertising to other members.

He added that Megan herself violated MySpace's age limits by creating a profile when she was under 14. "No one would seriously suggest that Megan's conduct was criminal or should be subject to criminal prosecution," Wu wrote.

A host of outside organizations and individuals including the Electronic Frontier Foundation, Public Knowledge and law professors had filed a friend-of-the-court brief asking Wu to dismiss the charges before trial. Drew's lawyer also unsuccessfully asked Wu to throw out the case before the matter went to the jury.

The U.S. Attorney's office hasn't yet decided whether it will seek to appeal the decision. Any appeal would have to be approved by U.S. Solicitor General Elena Kagan.

Authorities in Missouri investigated Drew shortly after the suicide, but concluded that she hadn't broken any laws in the state. Last year, lawmakers enacted a new cyberbullying law that makes it a crime to cause emotional distress to someone via the Web, text message or other electronic forms of communication.

Law enforcement officials recently brought the first felony charges under that law. In that case, 40-year-old Elizabeth Thrasher is accused of posting photos of a 17-year-old girl -- as well as her email address, cell phone number and place of employment -- on Craigslist's casual encounters section.

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