National Security Agency whistleblower Edward Snowden answered questions from Canadian students on Monday, telling them that mass surveillance can actually harm the ability to prevent terrorist attacks while also being detrimental to personal privacy.

Speaking at Upper Canada College in Toronto via webcam from Russia, Snowden was joined by journalist Glenn Greenwald as the pair fielded questions from high school students. When asked about mass domestic surveillance – which new reports show Canada is engaged in – Snowden argued that the practice could divert attention and resources from more focused efforts that would yield better results.

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