Foreign exchange students in Russia have been warned that they are "soft targets" after a Cambridge undergraduate was fined for giving a feminism talk on her year abroad.

Harriet Phillips, 21, was visiting friends in the Siberian city of Krasnoyarsk when she was invited to informally address some 40 people on subjects including the patriarchy and gender stereotypes.

But fifteen minutes into the talk she was interrupted by three men - one of whom she claims was an FSB agent - who filmed her speaking then ordered that the computer operating her presentation slides be switched off.

The audience was told there would be a "technical break" while the officials from the Federal Migration Service told Miss Phillips she had breached Russian migration law because her tourist visa did not permit her to give educational talks.

Miss Phillips, who was on an exchange programme at St. Petersburg State University, insisted it was an open meeting and the talk was simply a warm-up before a group discussion.

But she was questioned for four hours and fined 2,000 roubles (£25). One of the officers admitted they would not have detained her if she had been talking about the weather rather than feminism.