http://www.bbc.co.uk/news/uk-england-berkshire-14897948 13 September 2011 Last updated at 09:10 ET Sean Duffy case highlights murky world of trolling A man has been jailed for 18 weeks for sending abusive messages on social networking sites. Sean Duffy, from Reading, Berkshire, posted hurtful remarks on pages set up in remembrance of girls who had died. His victims were the bereaved relatives of people he did not know, and included the family of Worcester teenager Natasha MacBryde who killed herself after being bullied. Duffy pleaded guilty to two counts of sending a communication of an indecent or offensive nature. The charges related to Facebook and YouTube posts about Miss MacBryde, 15, who Duffy had never met. But exactly what constitutes trolling, who does it, and who does it affect? Trolling is described by Oxford Dictionaries Online as an "informal term". It means to send or submit a provocative email or posting with the intention of inciting an angry response. Fevzi Turkalp, a technology expert from gadgetdetective.com says trolling is often used in chatrooms and online forums, especially in the technology world. "Someone will go onto an Apple website and say something derogatory about Apple, knowing full well people on there will be fans of Apple, in order to provoke a response," he said. However, there is a darker side to trolling, in which people take advantage of anonymity to make hurtful and offensive remarks. Cyberbullying "People feel protected by anonymity and the true nature of people comes to the fore," said Mr Turkalp. It is at this point that trolling can also descend into cyberbullying. Cyberbullying is defined by Mr Turkalp as "a repetitious and malicious activity by one person or a group of people against another individual". In the case of Miss MacBryde, her bereaved family and friends were targeted by Duffy's trolling. Duffy posted messages on a remembrance page set up by Miss MacBryde's friends. In one of the posts he called the teenager a slut. He also posted a video on YouTube, entitled Tasha the Tank Engine, showing the children's character Thomas the Tank Engine with Miss MacBryde's face. Miss MacBryde had thrown herself under a train after being cyber-bullied in a separate incident. In another cyberbullying case, Carney Bonner, 17, told BBC Berkshire in March how he almost "slit his wrists" due to being bullied on Facebook as a 14-year-old. And, although it is commonly believed that teenagers are the main victims of cyberbullying, teaching unions also report a rise in incidences against staff. Chris Keates, General Secretary of the NASUWT, the largest teachers' union, said pupils had started to use "sophisticated tools" against teachers. "Misuse of internet sites can destroy teachers' confidence and professional reputation and provide yet another vehicle for false allegations against staff. "New cases of abuse, harassment and humiliation are emerging all the time."