The BBC looks at five things we learned from the first live interview with a serving head of Britain's home agency MI5.
Andrew Parker told the BBC's Today programme that encryption was making monitoring online terrorist communication more difficult.
Ministers are preparing legislation on the powers for carrying out electronic surveillance.
Produced by Trystan Young
Read more http://www.bbc.co.uk/news/uk-34282449#sa-ns_mchannel=rss&ns_source=PublicRSS20-sa
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