What are tracking cookies on my computer?

Q Every time I run a security scan with my anti-virus program, it reports a number of tracking cookies on my computer, with names such as ‘John@double-click.net’. Should I be concerned that these are appearing on my PC, and is there any way I can stop them?

John Fullerton

A A cookie is a small file stored on your computer by a web browser, that contains information about your visit to a specific website. It might hold details about when you last viewed the website, your viewing preferences, or products you recently clicked on.

It may also record your IP address, the time of your visit and the browser you use. Cookies are harmless, since they are no more than a text file, and without them some aspects of the web, such as shopping carts, would not work properly.

Tracking cookies are slightly different. These are cookies placed on your computer by a website affiliated with the one you visit, and are sometimes called third-party cookies. Often this is a company that provides adverts for multiple websites, such as Doubleclick.

These companies’ websites can use tracking cookies to build up a picture of your web surfing habits. It cannot track every site you visit, only those that carry that company’s adverts.

While some people see this as an invasion of privacy, these cookies are not the same as other malicious software, and cannot infect your PC. Don’t worry about them too much, as they are used in a lot of places and, after visiting a number of websites, it’s almost inevitable a few will end up on your PC. But it doesn’t hurt to remove them if you wish.

Alternatively, you can prevent them being downloaded in the first place. All browsers have options to restrict the downloading of cookies. In Internet Explorer 8, you can do so by clicking on the Tools menu, then clicking on Internet Options.

Click the Privacy tab and adjust the slider on the left. At its maximum setting, no cookies will be created on your PC but, as we mentioned, this may cause problems, we recommend using a slightly lower setting.

One possibility is to allow first-party cookies while disallowing third-party cookies, which is unlikely to cause problems when using certain aspects of websites, but will stop sites placing tracking cookies on your PC.

Under the same privacy tab, click the Advanced button, tick the box to override automatic cookie handling, and set third-party cookies to be blocked (or prompt if you wish).

If you run into a site that says you need cookies enabled to view it, click the Sites button in this options window, and enter the URL of the website, so it ignores the rules you just set up.

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