Cookie poisoning is a known technique mainly for achieving impersonation and breach of privacy through manipulation of session cookies, which maintain the identity of the client. By forging these cookies, an attacker can impersonate a valid client, and thus gain information and perform actions on behalf of the victim. The ability to forge such session cookies (or more generally, session tokens) stems from the fact that the tokens are not generated in a secure way. On the Web, cookie poisoning is the modification of a cookie (personal information in a Web user's computer) by an attacker to gain unauthorized information about the user for purposes such as identity theft. The attacker may use the information to open new accounts or to gain access to the user's existing accounts.