Polish students organized a lesson about cyber security. About 30 people from the exchange program took part in. The lesson began by dividing the students into groups of six and conducting a short test of knowledge about Internet safety. Next, we presented a short presentation about the basic principles of online security and possible threats on the web network. The next stage of our lesson was a film about manipulation, cyberbulling in social media. We finished the lesson with a second test to check if the students' level of knowledge increased after the lesson.