3. A method as in claim 2 , wherein obtaining the set of facts from the PIM server includes: finding a set of documents on the PIM server having a reference to the user identifier and a reference to another user identifier, and forming, as a fact of the set of facts, an aggregate fact from the set of documents; wherein generating the set of KBA questions from the set of user facts includes: generating a KBA question of the set of KBA questions from the aggregate fact.
4. A method as in claim 3 , wherein an attribute of the predetermined set of attributes is the number of documents of the set of documents from which the aggregate fact of the set of facts was formed; and wherein combining the fact scores assigned to the facts of the set of facts includes: weighting the aggregate fact by the number of documents of the set of documents from which the aggregate fact of the set of facts was formed.