Inside the cookie monster - trading your online data for profits The devices allow a third-party company to see which elements of a page the user has clicked on, potentially identifying information held in the URL, such as an email address. A tracking device, owned by Yahoo! and dated to expire in 2037, was planted on this website's test computer when visiting the website of the federal Opposition Leader, Tony Abbott. The site of the Premier, Kristina Keneally, placed devices owned by ShareThis, a company that collects information about online habits. All four websites planted YouTube cookies, even though this website's computer did not play any videos.

Outrage in the US over YouTube cookies placed by the White House's website last year prompted the company to develop videos that let publishers choose if cookies are planted. The websites of Ms Keneally, Mr Abbott and the Greens also planted flash cookies which can hold more data than standard cookies. They also have no expiration date and are stored on an external server, which makes them difficult for users to detect or delete. The NSW Liberal Party, which administers Mr O'Farrell's website, said it used analytic devices to find out which parts of its sites visitors were engaging with. The ALP said thousands of websites used tools such as Google and YouTube every day. "If there are any issues around the processes undertaken by ShareThis ... NSW Labor would be very interested in investigating,'' said an ALP spokeswoman. None of the websites mentioned third-party tracking devices in their privacy policies.

A spokesman from Mr Abbott's office said any questions about what third-party cookies collect should be directed to those companies. ShareThis and YouTube said users were able to delete or disable third-party cookies. The information these devices gather is considered anonymous because it identifies browsing software, not individuals. The Australian Privacy Commissioner, Timothy Pilgrim, said aggregated data might enable identification of individuals. A cyber law researcher at the University of NSW, David Vaile, said data collectors were developing extremely sophisticated tools. ''Unless you've got a detector or know what you're looking for, you won't know they are there.''

Do you know more? nphillips@smh.com.au