Increasing numbers of teachers are becoming victims of cyber-bullying from both pupils and parents, a teachers' organisation has said.
Incidents range from abusive emails to the malicious use of websites and chatrooms, it said.
Silent phone calls and unwelcome text messages were also reported by some of those teachers surveyed.
The Teacher Support Network and the Association of Teachers and Lecturers carried out the research.
Its director Mark Langhammer said anti-bullying policies needed to be introduced.
"Certainly in Northern Ireland, the Department of Education have not issued a general guidance to schools," he said.
"Some schools have very good policies, some have none at all. Teachers very often are working in a vacuum."
Fern Turner from the National Association of Head Teachers' said it was a hard problem to tackle.
She said: "There are teachers whose whole professional reputation is being challenged on these sites.
"What we are told is that the network providers monitor the sites and take off material which they feel is inappropriate.
"While people can say anything and write anything, the victims can't actually address or challenge it."