Publishers detecting whether online readers are using ad blocking software are contravening European data legislation, according to a privacy expert.

Alexander Hanff, a privacy consultant at Think Privacy, made the claim in a panel debate on the opening morning (18 April) at Advertising Week Europe in London.

Richard Eyre, chairman of the UK arm of the Internet Advertising Bureau (IAB), opened the session by reiterating the claim that ad block users are “stealing” content from publishers.

However, Eyre acknowledged that the “tacit agreement” governing digital publishers’ relationship with consumers – namely that users accept ads as a free alternative to subscription models – has been wiped away, and that publishers must “fix the aircraft while in flight”.

“This is clearly not a moral issue for anyone, and we can’t make it one. We cannot stop that wave, but we can imagine new business models. That tacit agreement is gone,” said Eyre.

The Guardian’s global revenue director Tim Gentry agreed that publishers must encourage users to make a more “cognisant decision” to accept advertising in exchange for content: “This is probably one of the most material disruptions I’ve ever seen. The level of volume it represents, [users are] pointing a gun at the industry and saying, ‘What you’re doing is not acceptable to us.’

“It is a wake-up call for all of us, to reinvent the way we treat our relationships with audiences. The value exchange has been so implicit, need to bring that more into a cognisant decision,” added Gentry, referencing his newspaper’s move towards a membership-based premium subscription model.

Ben Williams, operations and communications manager at Eyeo, the company behind the world’s most popular ad blocking software, Ad Block Plus, insisted that his company was not guilty of “racketeering” and praised the IAB’s ‘LEAN’ initiative to encourage more user-friendly ad formats.

The real controversy arose when privacy expert Hanff argued the IAB’s accusation of ad block users as being thieves is “harsh to say the least”, and insisted publishers like The Guardian and Forbes needed to look closer to home about the legalities of their own policies.

“Legally [users are] allowed to block advertising in the UK, so accusing them of being criminals is not relevant,” says Hanff. “[But] detect if a user is using ad blockers convenes European data law. You need consent. Websites like The Guardian are technically illegal and in breach of the Data Protection Directive.”