Sequence Number Spoofing

TCP/IP network connections use sequence numbers. The sequence numbers are part of each transmission and are exchanged with each transaction. The sequence number is based upon each computer's internal clock, and the number is predictable because it is based on a set algorithm.

By monitoring a network connection, a hacker can record the exchange of sequence numbers and predict the next set of sequence numbers. With this information, a hacker can insert himself or herself into the network connection and, effectively, take over the connection or insert misinformation.

The best defense against sequence number spoofing is to encrypt a connection. Encrypting a connection prevents anyone who may be monitoring the network from being able to determine the sequence numbers or any other useful information.

Session Highjacking

Session highjacking is similar to sequence number spoofing. In this process, a hacker takes over a connection session, usually between a client user and a server. This is generally done by gaining access to a router or some other network device acting as a gateway between the legitimate user and the server and utilizing IP spoofing. Since session highjacking usually requires the hacker to gain privileged access to a network device, the best defense to take is to properly secure all devices on the network.