But even more students have likely been targets of such high-tech harassment, Marianne Demmer, vice president of German Education Union (GEW), said in Berlin.
Demmer, however, warned against dramatizing the problem of online bullying, saying that harassment without aid from technology is even more common. She urged schools to establish clear codes of conduct to help protect teachers and students from both forms of harassment.
"Student pranks and bullying are an old topic that has now made an appearance in the internet age," Demmer said.
The union cited an online survey of 488 members in which eight percent of teachers said they had been harassed at least once on their computers or cell phones. About a third said they were aware of similar cases in their circle of friends.
The union reached its estimate for the total number of teachers likely to have been affected by harassment by extrapolating the results over the about 700,000 teachers in Germany.
All age groups and grades were equally affected, the union said, and in about three-quarters of cases the teachers were being harassed by students.
Boys are "more likely to reach for a mobile or computer in order to put pressure or take revenge upon other students or teachers," Demmer said.
Some five percent of the harassment cases originated with supervisors or parents and three percent with colleagues.