Ethical dilemma: "defence" industry employers

I've just received a job description for a contract at a software company whose customers include a bunch of organizations in the killing business. Australian, New Zealand and Malaysian Navy, Australian "Defence" Industries, Boeing. I've always been adamant that I won't work in such industries. But where do you draw the line? In my line of work, the biggest employment sector tends to be in the death industries.

I believe this project is working on their evidence-management product. So this would be working in law enforcement type stuff, as opposed to baby killers. But the company definitely works in "defence", though they have nothing directly to do with making guns, bombs and the like.

So where does one draw the line? Quite a difficult one to decide. Your thoughts?