A contact information
database, including records such as those stored in a personal
address book, is applied to evaluate the reputation of a user and / or conduct fraud or spam detection. A number of different factors selected for reputation / fraud prediction value can be used in a
statistical model to evaluate reputation of an
individual based on an identifier, such as an
email address. The factors can include information useful in predicting the reputation of an individual, such as in how many address books the
email address or other information appears, whether emails have been previously sent to that
email address, whether any such emails have been returned as undeliverable, and so forth. These factors can be used to create a vector including scores for the user on the various factors, which can be stored in a vector
database and updated regularly as the information changes. The information in the vector
database can be accessed by parties for use in reputation evaluation, fraud detection, etc. for a particular email address or individual.