LOS ANGELES — A judge has finalized his decision to throw out convictions of a Missouri mother for her role in an Internet hoax directed at a 13-year-old neighbour girl who committed suicide.

U.S. District Judge George Wu said in his written ruling that the case was never a legal test of crimes involving "cyberbullying."

Prosecutors, who adopted that terminology early on, brought charges against Lori Drew under the Federal Computer Fraud and Abuse Statute which does not involve cyberbullying, the judge said.

Wu acquitted Drew of misdemeanour counts of accessing computers without authorization last month but stressed the ruling was tentative until he issued it in writing.

Drew's attorney, Dean Steward, believes Wu's ruling in effect strikes down a portion of the computer fraud act.

"He's pretty much found that portions of it are unconstitutional," said Steward, who expects Department of Justice attorneys to go back to Congress for a clarification.

Thom Mrozek, spokesman for the U.S. attorney's office in Los Angeles, said no decision had been made yet about a possble appeal.

Prosecutors say Drew sought to humiliate Megan Meier by helping create a fictitious teen boy on the MySpace social networking site and sending flirtatious messages to the girl in his name.

The fake boy then dumped Megan in a message saying the world would be better without her. Megan hanged herself a short time later, in October 2006, in Missouri.

Drew was not directly charged with causing Megan's death. Instead, prosecutors indicted her under the computer fraud act, which in the past has been used in hacking and trademark theft cases.

Wu's 32-page ruling, filed late Friday, cited vagueness of the statute and the chance that innocent users of the Internet could become subject to criminal charges if Drew's conviction was allowed to stand.

He gave examples of people who could be liable for violating MySpace rules online including "the lonely-heart who submits intentionally inaccurate data about his or her age, height and/or physical appearance," or "the exasperated parent who sends out a group message to neighbourhood friends entreating them to purchase his or her daughter's Girl Scout cookies," a violation of rules against advertising or soliciting sales.

Much attention was paid to Drew's case, primarily because it was billed as the nation's first cyberbullying trial. The trial was held in Los Angeles because the servers of the social networking site are in the area.