What are you asking?

You're in the "Office and productivity software" forum so am I to assume you are specifically interested in Office apps?

Is your question related to your other post here? http://forums.cnet.com/7726-6129_102-5313464.html

If not, what are you asking? Your own "Web application security testing" is a great term to use to start your search engine research, I just tried it.

Other than that, there are no key players in the field as you will find many companies and organisations looking at web security as well as governments.

However, you may want to start with Sophos and Kaspersky, and in fact Kaspersky's Mikko Hypponen is often featured in online security video discussions at F-Secure Labs own YouTube web site here;
http://www.youtube.com/user/fslabs

Have a look at Mikko's chat with F-Secure Labs' Sean Sullivan in that page or here; http://www.youtube.com/watch?v=WyAmC6DPRzw&list=UUdV8ZHnzZGfOc39IbhmRJ_A&index=8&feature=plcp where they discuss "Ransomware Trojans"

I hope that helps.

Mark