How seemingly innocent exchanges on text, Twitter and Facebook can lead to sexual and emotional entanglements between a teacher and pupil. Pupil-teacher affairs are as old as education. Some end up in court and prison, others in love and marriage. There are now estimated to be over 1,000 illicit pupil-teacher relationships every year. Like the global headline-making case of 30 year-old music teacher Jeremy Forrest and his 15 year-old student, many of these affairs start with a simple 'x' at the end of a message.