Just blurt it out casually in the beginning, "Oh, I work in porn.".
You can then even take it a step further, and act as if you're an actor in porn flicks. After having some fun with the role-play, you can just assure her that you only develop and own some websites. An entreprenur. She'll probably be relieved.
If you're secretive or ashamed of it, it will never work. That will make you seem like a shady and not confident person, which is very unattractive to girls. Being a truck driver can also be a great job, or a shit one - it's in the eye of the beholder. If you're a confident, happy man, and she's open-minded, she'll have no problem with it. I find it that it's even exciting to many girls.
If porn is very much against her morals, she would be a waste of time to you anyway. It's better to find out early.
If she's interested in what you do, you should explain to her what kinds of things you do on a day-to-day basis. When she realizes that running a porn site is more like a boring, administrative, office job, than a drunken fuckfest, she'll probably view it differently.