Is there a standard governing the __utma, __utmz etc.. cookies?

Whether I log into Faceb开发者_C百科ook or Twitter, I'll be bombarded with cookies of the such names as:

__utma
__utmb
__utmc
__utmv

What are their functions ? Is there a standard that governs how these are used on the serverside ?

These are cookies generally associated with Google Analytics.

See this info from Google itself.

BTW, the UTM prefix originally stood for Urchin Tracking Module, whereby Urchin Software Corp is a company acquired by Google in 2005 and which product was used as the basis for Google's initial offering in the Web Site Analytics market.

These are cookies that come from Google Analytics. I couldn't immediately find the reference in Facebook's page source, but Twitter has it, and I've seen it plenty of times before in my own websites that use Google Analytics.

Here is an overview of the cookies Analytics uses.