In reality, though, cookies are very safe! Let's look at an example. This site - CacheKiller.com - maintains a cookie whose value is a single number between 1 and 12. Each time you click a button to go to a different page on the Cache Killer site, the number is increased by one until it gets to a value of 12. At this point, the number is changed to 1 and the process repeats itself. This data is used to cycle through the Tips and Tricks items that appear in the upper left portion of the window.

There are strict rules regarding how web sites may deal with cookies. First, a web site is only allowed to create cookies for its own site. The Cache Killer web site can create "cachekiller.com" cookies but not "yahoo.com" cookies. Second, a web site can only access its own cookies. Thus, we are allowed to look at our "cachekiller.com" cookie to see if the value is 1, 2, 3,… but not the "yahoo.com" cookie to see what stocks you are tracking in your portfolio.

So, in summary, we can only create "cachekiller.com" cookies and we can only view "cachekiller.com" cookies. That's tight security!

There is a privacy issue, though, if someone else accesses your computer. Cookies are owned by a particular web browser on a particular computer, not by a particular user. Thus, John can setup his portfolio on Yahoo and be comfortable that we at Cache Killer won't get hold of it, but his roommate Sam won't have any trouble viewing it.