Reuters Business Report - The Edward Snowden affair highlighted the issue of cyber security.
It's also a key focus for the defence industry, says Scott Mc Vicar from BAE Systems Detica.
Scott McVicar, Strategy Director for Cyber Security, BAE Systems Detica:
"Cyber is in many ways the new and evolving front on the modern battlefield. And in many ways it's an intelligence-led engagement. The kind of tools that you see behind us here are all about presenting an intelligence picture in a way that our analysts can make best sense of the threat, help understand its intent and counter it as effectively and efficiently as possible."
Many western countries are cutting back budgets - it's the emerging ones that companies likes BAE Systems, Lockheed Martin, EADS and Finmeccanica are looking at at Defence and Security Equipment International.
Al Lockwood, Spokesman for DSEi 2013:
"What we have here is a showcase for industry. Industry comes from around the world, they bring their products here and other businessmen come to the show to talk and obviously look at how they can work together to produce defence and security-related products."
All countries which have diplomatic relations with the UK can attend - this year that's 1500 exhibitors from 40 countries.
South Korea and the United Arab Emirates are here for the first time.
And India has increased its presence - it has companies looking for new suppliers and ways to tap export markets.
The defence industry is a major employer in the UK.
But not everyone welcomes that. There've been daily protests outside the London venue.
Kaye Stearman is from the Campaign Against Arms Trade.
Kaye Stearman, Campaign Against Arms Trade:
"We have added up the jobs for whole military industries and they come to around 215,000, maybe fewer, and only about 50,000 of those are involved with arms exports. So yes, there are jobs involved but there aren't nearly as many as people imagine. It's about 0.2% of the UK workforce."
The prospect of Western action in Syria has put military might into the spotlight.
But a possible strike wouldn't necessarily lead to more deals, says defence analystHoward Wheeldon.
Howard Wheeldon, Defence industry analyst:
"Defence is a long-term product, it goes on for years. If you think about something today, you order in three or four years' time, you build it over a period of five or ten years, so it's a long-term industry. One event doesn't change anything."
Defence firms are quietly cautious - and it seems there are new buyers out there - just not where you you might expect.