When you go online, Google probably knows.

Key points: Google plans to eliminate third-party cookies by 2022

Google plans to eliminate third-party cookies by 2022 This will shake up the advertising industry, which uses them to target ads

This will shake up the advertising industry, which uses them to target ads Google says it's about privacy, but critics argue the company relies on advertising revenue

The company's web browser Chrome dominates the market, and that's why Google got a lot of attention last week when it announced it intended to change the way ads are targeted online.

Google's goal of making third-party cookies "obsolete" by 2022 will be a significant shift for the online advertising industry, which relies on the technology to serve personalised content.

"Users are demanding greater privacy…and it's clear the web ecosystem needs to evolve to meet these increasing demands," Justin Schuh, Google's director of Chrome Engineering, wrote in a blog post.

The technology giant claims this move will boost online privacy, but it comes as the company is under increased scrutiny for potential anti-competitive practices.

To understand this latest instalment in the great cookie debate, let's start with the basics.

What are cookies?

Cookies have a bad reputation — the little bits of information that follow us around online — but they were originally designed for more benign purposes, said Dr Leslie Sikos, lecturer in computing and security at Edith Cowan University.

He defined cookies as "plain text files that store user settings for a particular website".

First-party cookies might help keep you logged into a video streaming service, for example, or record your language preference.

But third-party cookies are typically created by a company external to the website you're using, and can often follow you online. Even if you have no idea they are there.

Say you're looking at gym memberships. These cookies could help an ad for your local yoga studio chase you across different websites.

How will this affect the web?

As the most popular browser provider, Google's decision will have a significant impact on advertisers.

Some suggest consumers will start to see less relevant ads. Others think marketing will just have to get cleverer. But most acknowledge the way third-party cookies currently operate creeps people out.

Google's move should come as no surprise, said Caitlin Lloyd, national head of strategy at Tribal Australia.

She pointed out that Apple began blocking third-party user tracking on Safari in 2017 (which also made some advertisers mad).

"Some brands are undeniably overly reliant on third-party cookies, particularly those with a heavy reliance on remarketing," she said, referring to the practice of chasing a customer who visited a website with ads as they browse elsewhere.

"It's the businesses that act like the guy who repeatedly asks for your number even when you've told him you're not interested that will be left behind."

It's also potentially "a smart move for Google", suggested Jason Davey, head of experience technology at Ogilvy Australia — and one that could push advertisers to the technology giant's search advertising services.

Currently, a third-party cookie might be sold to a media agency indicating someone is in a particular market category.

If you're looking at flights to Berlin, say, you might be served online ads for hotels in Berlin when you visit a news website.

Without third-party cookies, brands may instead turn more to 'search' advertising, he explained. So that when someone "googles" Berlin flights, the search results also display hotel options.

What's Google's bottom line?

Google says this decision is all about privacy, but it's still a for-profit corporation.

The company wants to figure out a way to show people relevant ads, but without handing over so much of our personal data.

But by eliminating third-party cookies, some US critics worry Google is favouring its own platform.

Remember that Google has a lot of first-party data about people, thanks to its services like Maps, Gmail and even its smart home devices.

"Google and Facebook are both safe in this equation," said Victor Condogeorges, director of data and insights at Orchard.

"They don't consider their [own] data 'third party'."

Like Google, Facebook is dominant in the online ad space. ( Reuters: Dado Ruvic )

While enhanced online privacy is welcome, there are still many unknowns about Google's new approach, said John Broome, chief executive of the Australian Association of National Advertisers.

"It is crucial that any approach taken by internet browsers continues to facilitate healthy competition in advertising services," he said.

A spokesperson for the Australian Competition and Consumer Commission, which recently scrutinised Google's market dominance, said it was aware the decision may have implications for other businesses.

"Including potentially for Google's rivals in the ad tech supply chain which use data to assist in the delivery of targeted advertising," he said.

The agency encouraged concerned stakeholders to get in touch with the ACCC.

So, is this good for my privacy?

If you use Google's web browser, the upcoming end of third-party cookies may be good for the security of your online information.

But overall, Dr Sikos said using Chrome remained "one of the worst choices when it comes to user privacy" because of the company's own tracking.

Google monetises the activities of its users — whether on search, browsers or elsewhere — via its advertising business.

If you're concerned about this, Dr Sikos recommends using a browser from a vendor with a reputation for not collecting user data for targeted ads, such as Firefox, as well as a reputable privacy protection (anti-tracking) plugin.

"It is actually very ironic, because this company is the biggest tracker of them all," he said.

Google was contacted for comment.