Abstract: A network device for monitoring and modifying data traffic between a client device and a server device is disclosed. The network device is configured to provide targeted advertisements to a user based on some or all of the data traffics generated the user. Different from a proxy server, the network device operates transparently from both perspectives of a computer being used by the user and a website being visited by the user. The network device is disposed in line between the computer and the network so that all data traffics are examined. The data packets exchanged between a computer and a website being visited are altered or modified in such a way that the head of the packets remains largely intact while the payloads of the packets are changed to suit the need of delivering transparently the targeted commercial information.