Webtrends Analytics 9 Adminstration Guide, November 2012
Whether web browsers are likely to accept a cookie strongly depends on whether the cookie is a first-party cookie or a third-party cookie.
A cookie served from a domain other than the domain that your visitor requests from your website is considered a third-party cookie. Webtrends Analytics 9 and SmartSource Data Collector (SDC) have historically used cookies as the primary method to obtain visitor information.
Tracking visitors accurately is paramount for confidence in your web analytics results. Studies by leading analyst research firms such as Jupiter Research and Forrester have indicated that increasingly high-rates of cookie rejection and deletion by Internet users makes third-party cookies an unreliable method for collecting and reporting on web marketing results. In fact, Jupiter currently believes third-party cookie rejection rates are as high as 28%.
In response, Webtrends conducted its own research, analyzing third-party cookie rejection rates for 5 billion visitor sessions between January 2004 and April 2005. Webtrends research found cookie rejection rates to be somewhat lower but still significant, revealing that on average 12% of Internet user traffic is blocking or preventing third-party cookies from being set on computers, and that this trend can be as high as 17% for some vertical industries, such as retail. In addition, when analyzing the third-party cookie rejection trend since the beginning of 2004, Webtrends findings show that third-party cookie rejection has increased by a factor of four to its current rate.
Internet users commonly reject third-party cookies as part of their security measures. Some of the most common reasons for the increase in the rejection of third-party cookies are:
Anti-spyware programs are designed to remove cookies that surreptitiously monitors visitors' web activities. These programs often consider hosted web analytics services to be spyware and thus target their cookies for removal from your visitors' computers.
Current browser technologies such as Microsoft’s Internet Explorer and Mozilla’s Firefox make it easier for visitors to reject third-party cookies.