Behavioral advertisement targeting and creation of ad-hoc microcommunities through user authentication

Implementations of behavioral advertisement targeting and creation of ad-hoc microcommunities through user authentication are described. In one implementation, a user is allowed to submit authentication information on a webpage associated with a third party website. For example, a user can identify himself by entering a username and password to an email account unaffiliated with the third party website. The authentication information can then be used to access a personal account associated with the user. For example, behavioral data associated with the user can be gathered from the personal account and be used to present advertisements on the webpage targeting a specific behavioral profile of the user. Alternately, the user can be presented with options to interact with information in the personal account. For example, the user may be given the opportunity to invite members of a contacts list in the personal account to visit the webpage.