It's an addiction if it's a problem for him that interferes in his regular functioning. If you're going to discuss it with him that's good, in my opinion, because you need to have some understanding of boundaries with computer use through the whole family.
In our family it's husband who is the boss of the box, to a large extent. He includes us all in the discussion but is the one "on watch" so to speak, checking logs and scrutinising incoming emails and pop-ups. When he sees a problem in the making he goes to whichever family member was the likely cause and sorts it out.
During the recent film with autistic kids, the parents were sharing email addresses. I unthinkingly gave out ours, to suddenly find that one of the parents had set them all up on a yahoo mailing list which was open to the world! It was like a broadcast announcement to all the spammers, "Come on, guys! here are some free email addresses, live, ready and waiting!"
husband was really angry about it and when I spoke to the person who had done this, she said, "But the list is only for us - people have to sign up to get access to the list. I think he's being a bit paranoid, don't you?"
I told her about how his work email regularly collects about 100 messages overnight, mostly spam. She looked sceptical (bit I know it's true - I've seen it). I decided to not bother explaining, that spammers can sign up too, simply to collect the list. In fact, it's what a lot of them do, with something as wide open as Yahoo. We even got our family hacker to test our new ultra-private email address to make sure it was untrackable and uncrackable. Luckily I hadn't given this woman THAT one!
I know it sounds like I've gone off topic, but what I'm trying to say here - you sound like the equivalent of my husband - the family computer watchdog. If your husband has been surfing the dark side of the 'Net (as my husband does, both in the line of his work and in other areas, for curiosity) and he DIDN'T know enough to cover his tracks properly (ie he didn't know he was exposing you to pop-ups and spam) then he won't be able to do much better, even if alerted.
So if he pleads wide-eyed ignorance and the problems continue, make sure you have his OK to find out if it's your daughters. Don't give him details as to how you'll check, just say you'll "try and find out" if it's the girls. "Is that OK, husband?"
Of course he will say it is. If he's innocent, he will be worrying about what the girls may be up to. And if he's not innocent, he will be wanting you to THINK it's the girls.
He may be more careful - if all he's doing is dabbling in minor stuff out of idle curiosity, he'll probably stop. And you won't have anything to find.
But at least you will have his OK to do whatever you need to do to protect your family's computer.
There are so many things that can go wrong, if someone in the family is inappropriately using the computer. Identity theft, bank fraud, some nasty scams - they're the tip of the iceberg.
And if he STILL doesn't get it and thinks surfing the 'Net is harmless, get him to read "The Blue Nowhere" by Jeffery Deaver. He may never touch a keyboard again!
Mind you, if it turns out to be one of your girls, get THEM to read the book.
But I do agree with the others - the first thing to do is talk about it. And the main reason for tracking (if you feel it's necessary) should be primarily to protect the family from the fallout of careless usage. If you feel that your husband isn't being honest with you, after all you've been through together, that is a separate issue. And talking is always the best way.
Fran, I like the way you connect watching sport and viewing porn - I see both obsessions as fantasy, idle curiosity with the unattainable. In a way, with both the viewing/watching can replace the doing, which is where it becomes unhealthy (as in, couch potatoes not exercising; porn-obsessed males needing a reality check). I don't have a huge problem with men viewing porn, mild and in moderation - I guess because I used to work with men who had girlie posters all over the walls. I just stuck up my own all-male posters to remind them that they weren't the only gender in that workplace.
But with both, moderation is important, for the sake of health.
Honey, talk to him. And if you feel you can't, THERE is the problem. What you're concerned about now is only the outward symptom. But I do feel you need to emphasise healthy computer use, for the safety of the family.
Marg