How to express you are not familiar with a field
If you're completely ignorant of the subject, you ought to say:
I'm unacquainted with computer security...
or
I'm unfamiliar with computer security...
In a comment, Jim wrote:
I’d probably say that I was not well-versed in computer security and I’ve searched for the term.
If you're not well-versed in something, you don't know much about it.