The recent post "Danish military intelligence uses XKEYSCORE to tap cables in co-op with the NSA" - https://news.ycombinator.com/item?id=24960994 https://news.

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