1. A method of producing a custom behavior credit score for use in credit decisioning for an account at a financial institution, the method comprising: assigning an account to a segment from among a plurality of segments of accounts at the financial institution, wherein each of the plurality of segments of accounts have a different associated custom behavior model so that segmented accounts will have a different customer behavior score based on which segment each segmented account is assigned to, wherein each custom behavior model uses transaction attributes, masterfile attributes, and credit bureau attributes; updating, by a computer hardware processor, the plurality of custom behavior models, each custom behavior model using masterfile attributes, credit bureau attributes, and transaction attributes, wherein the transaction attributes comprises data gathered through monitoring, over a period of time, patterns of transactional behavior of a customer, and wherein a different custom behavior model is associated with each of the plurality of segments of accounts at the financial institution; and determining the custom behavior credit score for the account from the custom behavior model associated with the segment to which the account is assigned, said custom behavior model using transaction attributes, masterfile attributes, and credit bureau attributes in determining the custom behavior score for the account, wherein at least some segments from the plurality of segments of accounts are determined by grouping accounts into a plurality of clusters based on Euclidean distance between points in a multidimensional space, wherein each point represents one of the plurality of accounts, and each dimension in the multidimensional space represents the transaction, credit bureau, and masterfile attributes, and wherein the assigning the account to a segment comprises determining a Euclidean distance for a point representing the account from a centroid for at least some of the plurality of clusters.