A teenager has been detained for three months in a young offenders' institution for harassing a woman on social networking website Facebook.
Keeley Houghton swore at and threatened Emily Moore in person and on the internet in July, Worcester Magistrates' Court heard.
The 18-year-old of Elgar Avenue, in Malvern, Worcestershire, admitted a charge of harassment on 31 July.
She was also given a five-year restraining order.
Houghton is prohibited from contacting Ms Moore, or commenting about her on any social networking system or website during that time.
Emma-Jane Cross, chief executive of charity Beatbullying, said the sentencing was the first of its kind in the UK.
She said although cyber-bullying is increasing, the government, networking sites like Facebook and charities should work together to tackle the problem of bullying generally.
"Today's sentencing of an 18-year-old girl for cyber-bullying is the first of its kind in the UK and sets an important precedent," she said.
"Cyber-bullying is a worrying and fast-growing trend which can be more harmful than typical schoolyard bullying.
"However, the solution is not to limit young people's internet access and phone usage.
"Instead, social networking sites like Facebook, along with the Government and charities like Beatbullying, must work together to tackle the real root of the problem - the bullying itself."