The recent post<p>"Danish military intelligence uses XKEYSCORE to tap cables in co-op with the NSA" - <a href="https://news.ycombinator.com/item?id=24960994" rel="nofollow">https://news.ycombinator.com/item?id=24960994</a><p>has comments about the value of meta-data, and reminded me of the linked blog post 'Using Meta Data to Find Paul Revere'.<p>The blog walks through using matrix multiplication to identify 'suspects', and is a great introduction to social network analysis.