Questions about the cookies WordPress sets?

I wrote a lengthly post, “TUTORIAL: Filtering Yourself from Google Analytics” about how to set a cookie and setup a filter for Google Analytics so that you may filter yourself and your contributors form your sites statistics.

It was suggested that I write a Codex entry for this subject, in preparing for this project I am trying to round out the information to make the entry more accurate.

I am trying to understand the cookies that a WordPress site sets. As a viewer visiting a site you will find in your cookies, for the name of the site, 4 cookies will be set: _utmc, _utmb, _utma and _utmz. _utmc will have a 6 digit number for its content and the other 3 will have this same number at the beginning of each cookies content, followed by a dot and other values.

I have learned, through testing, that this number is unique to each site ( I think ). I have also learned that the number is added to any custom cookies you set which may be a problem.

Google Analytics requires a custom cookie be set with a value that you then filter out of your profile report. Unfortunately, or not, this 6 digit number is appearing in the value of the custom cookies before the custom value, with a dot between. This cookie is _utmv.

Went through the Codex but found nothing on this issue, in regards to none logged in, viewer cookies who just visit a site.

Can anybody, tell me anything about this number, why it is set and why it is being inserted into a custom cookie?

Thanks.