A computer implemented method, apparatus, and computer program product for port scan protection. A reply data packet having a modified transmission control protocol header is generated to form a modified reply data packet, in response to detecting a port scan. The modified reply data packet will illicit a response from a recipient of the modified data packet. The reply data packet is sent to a first Internet protocol address associated with the port scan. A second Internet protocol address is identified from a header of the response to the modified reply data packet. The second Internet protocol address is an actual Internet protocol address of a source of the port scan. All network traffic from the second Internet protocol address may be blocked to prevent an attack on any open ports from the source of the port scan.