Curbing hate speech on social media and internet platforms is particularly challenging, not only from a technical point of view, but also from a human rights perspective. While states have a positive obligation to prevent undue interference with civil and political rights by third parties, undue online regulation can easily result in undermining freedom of expression on Internet. In particular, the blocking and erasing of illegal content on the Internet in order to combat hate crimes must be grounded on precise and narrow definitions of the offences, be necessary in a democratic society and strictly respect the proportionality principle. Furthermore, effective judicial review by independent and impartial courts must be guaranteed.