A 49-year-old Missouri mother was yesterday found guilty in a landmark cyber-bullying case stemming from the suicide of a teenager who killed herself after being sent taunting emails, the Australian newspaper reports today.

Lori Drew was convicted on three misdemeanour counts of illegally accessing computers without authorisation but jurors in a Los Angeles federal court could not reach a verdict on a charge of conspiracy.

Prosecutors said Drew faced up to three years in prison and a $US300,000 ($460,000) fine, although no sentencing date had yet been set.

Drew, who showed no emotion as the verdict was read out, was charged following the tragic death of 13-year-old Megan Meier, who committed suicide in 2006 at her home in St Louis, Missouri. Prosecutors said Drew, her daughter and a family friend who were not charged, posed as a fictitious 16-year-old boy named "Josh Evans" who befriended Megan via a bogus account on social networking site MySpace.

Megan, who Drew suspected of spreading false rumours about her daughter, hanged herself after receiving a message from "Josh" that said the world would be a better place without her, the trial heard. The case was the first criminal prosecution in US legal history relating to allegations of cyber-bullying. Megan's mother described Wednesday's verdicts as a victory. "This is not about vengeance," Tina Meier said. "This is about justice for Megan and making sure this does not happen to anyone else. I don't want another family to have to endure this."

Federal attorney Thomas O'Brien said during the trial that Drew targeted Megan, even though she knew the teenager was vulnerable.

"The defendant knew Megan Meier was depressed, suicidal and boy-crazy," Mr O'Brien said. Nevertheless, Drew set out "to tease, embarrass, humiliate, make fun of and hurt her", he said.

Mr O'Brien said the case would serve as a warning to those who regarded the internet as a lawless environment.

"There have to be stronger laws against this (sort of behaviour)," Mr O'Brien said.

"People think they can do anything they want on the internet and they can't. If you're not watching what you're doing, you'd better be."

Drew's defence lawyer, Dean Steward, described the case as "deeply tragic".

"There's no satisfaction in any of this," Mr Steward said. "This is a deeply tragic case."

Prosecutors in Missouri had declined to bring a case against Drew. The case was prosecuted in Los Angeles because Fox Interactive, the owner of MySpace, is based in Beverly Hills.