Many years ago I investigated the UTM (Urchin Traffic Monitor). The Urchin Software Corporation developed this website traffic analysis tool for web masters. The tool analyzes the content in the web server's log file and creates traffic information statistics on that website based upon the log data.
Google purchased the company in 2005 and formed Google Analytics (GA). Google retained the name "Urchin" and designated the cookies as utm_.
Back then, I discovered that in addition to DSL Reports, the Internet Storm Center (isc.sans.edu), and the Christian Science Monitor (csmonitor.com) also use this analysis tool. In corresponding with the Center and csmonitor.com, I found nothing terribly invasive about this, so I forgot about it. It helps the web master manage the site.
Contrary to what some think, the cookie doesn't track the user from site to site, since it is not a 3rd party cookie (if we can believe the source):
Cookies & Google Analytics on Websites
»developers.google.com/analytics/ ··· es?hl=da
Google Analytics sets or updates cookies to collect data required for the reports. Additionally, Google Analytics mainly uses first-party cookies. This means that all cookies set by Google Analytics for your domain send data only to the servers for your domain. This effectively makes Google Analytics cookies the personal property of your website domain, and the data cannot be altered or retrieved by any service on another domain.