Abstract: Methods and systems for detection and estimation of fraudulent online advertisement attribution are disclosed. A plurality of network domains and a corresponding plurality of network locations for each network domain are determined based on network traffic data associated with webpage ad placement. The number of the plurality of network locations corresponding to each plurality of network domains is greater than a first threshold value. From the plurality of network locations, a second plurality of network locations is determined in which each network location is associated with two or more network domains of a predefined set of network domains. The number of the two or more network domains exceeds a second threshold value. A report is generated indicating the second plurality of network locations.