I. Introduction
With the explosion of Internet the occurrence of cyber terrorism has grown very rapidly. It is difficult to find and close all security flaws in a computer system that is connected to a network. Innovative and savvy hackers always find ways to break system security. Password sniffing and session hijacking, for example, are two of the common methods of system intrusion [1]. In these cases, the system under attack cannot even differentiate an attacker from a legitimate user. After an attacker maliciously updates some data items in a database, due to the durability property of transactions, [2], [3], [7], [9], when the transaction commits, its effect becomes permanent in the database and is made available to other users. In this way, the damage can spread to other parts of the database through legitimate users as they update fresh data after reading any damaged data [6], [17]. Hence, it is quite essential to perform immediate damage assessment and recovery to stop propagation of damage.