Sure, they can detect ad blockers and present a nag screen. The ad blocker can respond by defeating their detection feature. For example, it can delete the detection function before it even executes. They could circumvent that; ad blockers could nullify their fix; they could fix it again... This could go on forever.

In my experience as an user, no website has ever beaten an ad blocker. It's like trying to secure a computer against an adversary with full physical access. The content has left the server and is on the user's machine. Nothing can stop a sufficiently determined user from consuming it, with or without ads.

I answered a question on User Experience.SE about this:

http://ux.stackexchange.com/a/96907/3437

I tried to express just how big the power disparity between the developer and the user is. Looking back now, I think I came off as too extreme.

I think the other answers are excellent; they address the UX aspects in a way I wasn't able to. Definitely learned from them.

>It's like trying to secure a computer against an adversary with full physical access.

It is literally that, in fact.

I think back in the early days Hulu served their video and ads from the same url format, so you couldnt distinguish. That's not how they do it now, but back then it successfully defeated adblockers.

For example, if you were watching a TV show, it would give you a playlist of video segments and ads, all having random urls (hulu.com/<uuid>). You couldn't tell which was an ad and which was the real video, so adblockers couldn't write rules to block them.

VCRs with automatic ad-skipping (during playback or recording) appeared in the 90s, and had many orders of magnitude less processing power than even a typical smartphone today. They had to deal with ads embedded directly in the video stream, and worked reasonably well. Perhaps a similar approach will work very well with digital video today.

https://en.wikipedia.org/wiki/Commercial_skipping

If a site declares that you should not access it without disabling your adblocker, and they go as far as to explicitly try to prevent your access with direct messaging (interstitials, pop-up/light boxes, etc.), yet the user then works around those protections and accesses it - wouldn't that qualify as illegal access in some form?

How so?

A user requests a data stream, and receives it. That the user chooses not to execute or render a part of that stream is up to them - the data has already been delivered.

Interstitials, pop-ups and the like are simply contained within the stream, and aren't even guaranteed to run inside the browser. If the data connection is incomplete, modern browsers often discard data that is incomplete. Is that also illegal access?

The data stream is in the user's hands - and it is delivered before any Terms and Conditions are given.

It's similar to someone giving you a burger, saying it's free, waiting till you take the first bite, and then demanding that you eat the rest whilst they photograph you, and then use said photos to pay for making the burgers.

You could just walk away with your free burger.

Anticircumvention laws may or may not apply. I'm not sure. It certainly sounds like it does. The thing is I don't think those laws are very successful at preventing anything.

They didn't save the music records, movies and video games industries. They're still actively fighting against the user, an adversary that has all the power. DVD content was successfully decrypted despite the DMCA; ironically, genuine games are often inferior to their pirated counterparts. A site without ads has better usability and is more secure.

Even if sites say you can't access content already transmitted to your computer unless you view ads, they're not in a position to enforce that. A bunch of laws saying people can't circumvent their protection won't suddenly change that fact.

It's a cat and mouse thing. If they add some js to check for ad blockers then ad blockers block that too.

They could check over time if a user has seen as many ads as page views and block them then but users would just need to delete their cookies.

Until recently I've not had problems using ad blockers but in the last month http://www.telegraph.co.uk/ has become good at telling if I'm using one and not returning content if so. I wonder if this is the start of a more general fight back.

I guess as blockers stop ads downloading they just need to have something like an ad or an actual one and check if it's downloaded.

Sometimes it's a good thing. Often it gives me a few moments to pause and realise I really didn't need to read that article anyway.

Daily telegraph has recently switched to a stronger freemium model with a lot of premium content only visible to subscribers.

And you can be sure they pay a hefty sum for up-to-date anti-blocking software.