The Guardian reports that "despite the constantly evolving technological landscape that means more communications can be gathered and examined quickly, making sense of the material itself remains a primary obstacle to security." ...
"less than a quarter of MI5’s 4,000 staff are believed to be involved in analysis, and a far smaller number are sited among the 2,500 staff of MI6 – as few as 100, according to Davies. Although it is true that most of the 8,000 employees in GCHQ can be categorised as analysts, they have to evaluate a vast daily data stream that runs to countless terabytes. A single terabyte is the equivalent of 1,024 gigabytes, with a gigabyte the equivalent of 1.5 million WhatsApp messages."