A method of determining a risk score indicating a risk that an electronic transaction will involve fraud and/or abuse. The method includes receiving transaction data associated with a not yet completed transaction from a merchant. The transaction data includes one or more characteristics related to the transaction. A profile is selected that identifies network devices each associated with the characteristics and having a device reputation. Next, a profile-based risk factor is determined as a function of a percentage of the network devices having a negative reputation. The risk score is determined as a function of the profile-based risk factor. In some embodiments, a transaction-based risk factor may also be determined. In such embodiments, the risk score is determined as a function of the profile-based and transaction-based risk factors. The risk score is provided to the merchant to be used thereby to determine whether to proceed with the transaction.