Websites that use ad blocker detection software risk being "named and shamed" after a document reported to be from the European Commission suggested they were acting illegally.

Users who have installed ad blockers on their browsers in order to prevent adverts loading will have likely encountered websites that obscure access to content stating they have detected the software and require a user switch it off in order to browse.

In a letter sent to privacy campaigner Alexander Hanff, the EC revealed this ad blocker detection software requires access to users' personal data to determine whether they have installed tools to circumvent ads. Under EU law, publishers must ask for permission before accessing a user's personal information, much in the same way websites must ask for permission to store cookies on users' devices.

Specifically, article 5.3 of the EU's ePrivacy Directive states: "Storing information or gaining access to information already stored in the terminal equipment of a subscriber or user is allowed on condition that the subscriber or user concerned has given his or her consent, having been provided with clear and comprehensive information about the purposes of them processing."

Hanff claimed that as most publishers run anti-ad blocking script on users' browsers without prior consent, they are breaking the law. Hanff, who is CEO of privacy technology and services firm Think Privacy, now plans to launch a legal campaign against publishers using ad blocker detection in the EU and will set up a website to "name and shame" those found to be doing so.

A number of major publishers have employed mechanisms to deal with the rise in ad blocking software, which continues to threaten revenue gained from online advertisers. Conversely, some web browsers are beginning to make ad blockers a baked-in part of the experience in order to woo users.

Since announcing his intention to out publishers "illegally detecting ad blockers", Hanff claims he has received a "tidal wave of bile" from ad tech companies and has been threatened by the CTO of a large publishing group for "exposing their illegal practices".

IBTimes UK has contacted the European Commission for comment and will update this story as further developments arise.