The tracking cookies found by your virus software on your home pc are essentually harmless. However - if you are using a public pc you should allways delete all your cookies before your leave.

What is a Cookie?

A cookie is a simple, tiny, text file. It is stored on your PC, and is incapable of performing any tasks or functions. It is simply a text file containing data in text form, just like this (an example cookie from Google):

PREF
www.google.com/
1425
2053574882
30102496
3304564080
29955645
*

Cookies, once stored on your PC, are tied to a specific web address. When you revisit a web page, your browser checks to see if any cookies that are stored on your PC are valid ones for the page you are visiting. If they are, the information contained within them is sent back to the server.

Which means, essentially, that a website can only get from a cookie information it put there in the first place. Not all that dangerous in the vast majority of cases. With the above cookie on my PC, any time I visit a page within the "www.google.com" subdomain my browser will send the contents of the text file above to Google.

Tracking Cookies

In some circumstances cookies can be put to work in a wider context. Companies like "EuroClick", place tacking cookies on your machine. When you see an advert, that item may not necessarily be sent from the same server as the rest of the web page - it can be sent from another server. This is perfectly normal in the case of advertising providers. However, along with the advert, many advertisers also usually send a cookie set to use their main domain (eg "EuroClick.com").

The next time you request an advert from EuroClick your browser may send back data you received in a cookie from a previous time you viewed a EuroClick advert. One advertiser cannot read cookies from another, as web servers will only send cookie data out when you request a page from within the domain of the cookie.

This allows the advertiser to identify that someone who visited one page also visited another page. It can't identify you personally, but it can tell that someone who viewed a review of "Holden Vs Ford" on one site then went on to order 2 cartons of VBs at Liquor Barn - assuming both sites carry advertising from the same provider.

In the above example, if repeated by thousands of people, would tell the advertiser that people who like their Fords or Holdens also like to drink VB. They might use that information to help provide more accurate advertising - VB ads on the "Holden VS Ford" review, for example.

Is this dangerous? Not in the slightest.

Clearing Cookies on Public Computers

Cookies can contain your private information. Some poorly written websites use cookies to store your login details. If you are using a public computer, there could be cookies stored with your details. If you do not clear them, the next person at the computer may be able to view them.

So it is always good practice to clear or cookies after you have finished using a public computer.

To clear cookies on IE, goto to the menu bar and select Tools>Delete Browsing History... and click on the "Delete cookies..." button.

Looking for your Cookies?

You can take a peak of your cookies on your PC. You can find them by searching for cookie in the file manager.

• IE stores them in a cookie folder. C:\WINDOWS\Cookies
• Firefox stores them in a single file - either called "cookies.txt" or "cookies.sqlite". C:\Documents and Settings\user\Application Data\Mozilla\Firefox\Profiles