Webtrends Analytics 9 Adminstration Guide, November 2012
If you use Webtrends Analytics 9 or Webtrends On Premises with SmartSource Data Collector and you have multiple domains, your visitors will have a different first-party cookie set on each domain as well as a third-party cookie for your account.
These visitors are reported as unique visitors to each domain when you use first-party cookie session tracking methods. However, Webtrends can track your first-party cookies across domains by using the third-party cookie that identifies your domain.
You can create a separate profile to track your visitors across your domains using the Account Rollup data source, keeping in mind that this data source uses the Webtrends third-party cookie for tracking visitors. The visit and visitor counts are different when using this Account Rollup data source, compared to your more reliable first-party cookie profiles. However, it can provide you with meaningful insight into your account traffic if needed.
As a best practice, Webtrends recommends that you use first-party cookies to identify enterprise-wide, cross-domain behavior and trends. This method leverages a Webtrends third-party cookie to establish the first-party cookie, which tracks visitors across the specified domains in your data sources. If the visitor rejects third-party cookies, the first-party cookies continue to identify the visitor; however, that particular visitor appears as a different visitor for each domain.