"Security matters" means that the safety and protection of something or someone is important and should be given attention and consideration. Full definition
She has experience of national security matters and the special advocate procedure. (newlawjournal.co.uk)
I don't have a lawyer; for practical purposes, I am my own lawyer on securities matters. (alephblog.com)
In securities matters, he has represented venture capital investors, private placement companies and publicly listed issuers and has acted for underwriters. (mcinnescooper.com)