A router and method for preventing port scans using a router includes receiving a datagram from a remote computer, transferring the datagram to a local computer, and receiving a response datagram from the local computer. The router and method further includes dropping the response datagram if the response datagram is an Internet Control Messages Protocol (ICMP) port unreachable datagram and the ICMP port unreachable datagram is abnormal, and recording a port scan event of the remote computer into the log system.