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Privacy fact sheet 4: Online behavioural advertising — know your options

Companies use online behavioural advertising (OBA), also known as interested-based advertising, to try to match the ads you see while browsing online with your interests. Advertising and data collection companies do this by placing a cookie on your computer (cookies are explained below).

Interest categories, based on the sites you visit, are attached to these cookies and can allow advertisers to build up a picture of your browsing habits and interests. These interest categories can then be used to deliver ads. Some people don’t mind receiving ads that are targeted to their interests but it’s still important to be aware of how information about your browsing habits and interests is being collected and what your choices are.

The Privacy Act applies to ‘personal information’. Personal information is defined in the Privacy Act, but broadly speaking, it is information that can be used to identify you. The information collected by online advertisers may often not be sufficient to identify you; it might just be general information about your interests and sites you have visited. So companies using OBA may not need to comply with the rules in the Privacy Act about how personal information is handled.

However, it is important to remember that new technologies make it increasingly easy for the pieces of information that you provide when you are online to be combined. This process, called data aggregation, can provide a much clearer picture of who you are.

Did you know?

Many ads on websites are not placed there by the web site that you visit, they are provided by advertising networks which act as brokers, connecting web sites that want to sell advertising space with advertisers that want to reach potential customers. The same advertising network may deliver ads to many websites and may be able to track your browsing activities across many sites. The website you visit may also have its own analytics tools and trackers running to collect information such as the numbers of visitors to the site, how long they stay, and how they navigated to the site.

Know your browser

Different browsers have different settings and features that you can use to help control your personal information online. It’s worth checking out these options and comparing what different browsers offer, to decide what’s right for you. Common options include deciding whether to accept cookies and how long to allow them to stay on your machine. Some browsers also have additional privacy features that you can download and install.

Did you know?

Many browsers offer the option of browsing in ‘private mode’. This usually means that while this setting is active, your browsing and download history won’t be saved to your computer. It doesn’t mean that the browser will automatically block all tracking of your activities online.


A cookie is a small text file stored on your computer’s browser. Many cookies from websites will be visible from your browser. You will usually find information on cookies and how to manage them under ‘options’ or ‘settings’ in your browser. You can choose to see cookies before deleting them and to keep cookies from some sites.

There are several different types of cookies. A ‘first party’ cookie is sent from a web site to your web browser when you visit that site. This is how websites ‘remember’ things like your customised settings (eg your location), your shopping cart contents and your log in details.

Temporary cookies only last for one browsing session (until you close your browser), while persistent cookies remain on your computer after you close your browser and will be sent back to the web site each time you visit.

Third party cookies are sent by businesses that provide content, like advertising, on web sites that you visit. Many web sites feature advertising from third parties and those third parties may use cookies to track your browsing activities. As explained above, advertising and data collection companies can use this information to deliver advertising that they think may match your interests – this is online behavioural advertising.

Another type of cookie is the Local Stored Object (LSO), also known as a Flash cookie. These can contain more information than a regular cookie and are not generally cleared when you clear cookies from your browser. Depending on your browser, you may be able to install a plugin that will let you block or delete LSOs. You can also manage these cookies via the settings page in Adobe Flash.

Did you know?

Setting your browser to block all cookies may make some web sites take longer to load and stop you saving customised settings such as text sizes, location or login information. You can use the settings in your browser to control  how you deal with cookies, for example, you can choose to allow all first party cookies, to allow all first party temporary (session) cookies, to be asked whether you want to accept each cookie, or to block all third party cookies.

Opting out

Some companies that deliver OBA give users the options of viewing their profile, editing it or opting out of receiving targeted ads. Opting out won't remove advertising from the pages you visit; it means that the ads you see won't be matched to your interests. Sites that let you control what information is collected about you include Your Online Choices, Evidon Privacy Choice and Google’s Ads Preferences Manager. When you opt out of receiving targeted ads, this information is usually saved on a cookie. This often means that if you clear your cookies, you’ll have to opt out again. Some browsers are beginning to offer opt-out tools that won’t be affected if you clear your cookies.

Did you know?

Opting out of receiving targeted ads doesn’t always mean that information about your browsing habits won’t still be collected. For example, some options rely on advertisers signing up to an agreement not to collect information about browsing activities if people ask not to be tracked online. This will not affect advertisers who do not choose to be part of that agreement. There are other tools available, such as Ghostery Tracker Block and Better Privacy, that will help you see which trackers are active on pages that you visit and allow you to block them. Note that these tools will work differently depending on your browser.


The information provided in this fact sheet is of a general nature. It is not a substitute for legal advice.

For further information
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write: GPO Box 5218, Sydney NSW 2001
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