Some 59 scientists and university staff were threatened to such an extent last year that permanent or temporary measures had to be taken to protect them, university organisations have said in a new report.

In some cases their contact data had to be taken offline while others were moved to a safe house as protection, the report, which covers November 2022 to December 2023, said.

The threats varied from abuse on social media to intimidation on people’s doorsteps. Some academics, for instance, found stickers on their doors stating “we know where to find you”.

The universities have been monitoring threats to staff since 2022 and are in touch with police and the public prosecution office.

The university organisations said increasingly aggressive activists are prompting scientists to be more careful about talking publicly about their research, particularly in the fields of climate change, the war between Israel and Hamas and migration.

Caspar van den Berg, chairman of the Dutch universities association UNL, said the number and nature of the threats described in the monitor are “unacceptable”.

“It’s a horrifying experience for the people involved and alarming for society if scientists have to worry about their safety and become more reticent about their work,” he said.

“Now that scientific research is being doubted more and more, it is essential that scientists feel safe enough to communicate.”