Teachers should be wary of social networking sites and posting information on the internet amid concerns that schools and pupils are snooping online.

Headteachers and governors are googling potential employees, and students use the internet to find personal details about their teachers, a fringe meeting at the National Union of Teachers conference in Harrogate heard.

The union recently issued fresh guidance for members warning them against befriending pupils or parents on social networking sites, and to think twice before posting information and photos about themselves, or their school, that they would not want others to see.

Teachers could find that blurring the lines between their personal and professional lives could come back to “haunt” them, according to Amanda Brown, NUT assistant secretary for employment, conditions and rights.

There is now a general feeling that teachers have to worry about what is publicly available about them online, and if they are being watched by potential employers, pupils or parents, she said.

Karl Hopwood, an online safety advisor, told the fringe meeting he was aware of a number of examples where schools had checked up on teachers through the internet.

In one case, he said, a group of newly qualified teachers had had trouble gaining jobs, and the feedback they received from one headteacher was to look online.

One of the girls had a picture of herself with a pint glass on her head. After she removed the photo she got a job, Mr Hopwood said.

In another case, Mr Hopwood said he was part of an interview panel where the chair of governors handed him an envelope of information gathered from Google.

“It was of everybody going to interview and she said this was what they had found out about them.”

The chair had told him that they had to get the right person and if they could find out more information to help them, then that is what they would do.