Internet technology, because it provides a variety of services to clients which are physically located anywhere in the world, poses a challenge to designers of secure systems. The potential exists, anywhere on the route along which packets of a secure transaction are transmitted, for an intruder to access and perhaps even modify the transaction data packets.
It is not necessary to compromise the security of a router to have accesses to packets, one need only jeopardize the security of some host on a destination network on one of the legs along the route. Encryption of packets is a technique which may be used to protect the information in the packet. This removes most of the risk of packet access, however, modification of an encrypted packet will usually destroy the data in the packet and may disrupt the transaction.
The following sections contain a few of the many ways computer system security has been attacked, allowing an intruder to take administrative control of a machine or remove a machine from service. Either action is potentially disastrous for WEB based financial transactions.