1. A method of registering new users on cloud-hosted service sites, the method comprising the steps of: creating a database of electronically stored labeled records corresponding to known legitimate users registered on at least one cloud-hosted service site, each labeled record including fields corresponding to attributes associated with a legitimate user and values for at least some of the fields; creating a database of electronically stored records corresponding to individuals whose legitimacy as users of the cloud-hosted service is unknown, each unlabeled record including fields corresponding to attributes in the labeled records and values for at least some of the fields; creating a database of electronically stored records corresponding to individuals known to be malicious or undesirable, each unlabeled record including fields corresponding to attributes in the labeled records and values for at least some of the fields; computationally analyzing the database records to assign probabilities to at least some of the attributes and values, the probabilities correlating with a likelihood that a user is a legitimate user; receiving a candidate's request for registration, the request including values for at least some of the attributes in the databases; assessing the values in the registration request against the probabilities and computing a risk score for the candidate based thereon; and taking an action based on the risk score.