Google has changed its plans over the system it will introduce to replace cookies, sparking confusion and criticism across the advertising and tech industries.

A tracking system based on interest areas named ‘Topics’ will replace the previous ‘FLoC’ system.

Topics simply identifies a user’s interests, based on around 350 categories, such as NFL, fitness, or travel. This is a rotating list, which is stored and deleted each three weeks.

When someone visits a site, advertisers and the site owner will be served three interests from the visitor’s ‘Topics’ list. Sensitive interests will not be shared, and users can see and curate their own list, removing any that they don’t like – or simply disable the feature altogether.

FLoC offered a similar system: “developed with the idea to protect individuals’ privacy by placing them in a large crowd — a cohort — of thousands of people with similar recent browsing activity without any of them being individually identified,” according to Google’s original proposal.

This moving of the goal posts has advertisers worried.

“This constant indecision does not inspire confidence,” one exec told the BBC.

“The [FLoC] system was met with a lot of criticism when Google launched it,” Farhad Divecha, founder of digital marketing agency AccuraCast, said, “and it largely felt like a half-baked idea Google prematurely pushed out the door in response to changes in advertising and privacy.”

“The past year has made it fairly clear that Google still aren’t really sure of the best way forward.”