• E-mail hacking. Electronic mail is one of the most popular features of the Internet. With access to Internet e-mail, someone can potentially correspond with any one of millions of people worldwide. Some of the threats associated with e-mail are:
• Impersonation. The sender address on Internet e-mail cannot be trusted because the sender can create a false return address. Someone could have modified the header in transit, or the sender could have connected directly to the Simple Mail Transfer Protocol (SMTP) port on the target computer to enter the e-mail.
• Eavesdropping. E-mail headers and contents are transmitted in the clear text if no encryption is used. As a result, the contents of a message can be read or altered in transit. The header can be modified to hide or change the sender, or to redirect the message.
• Packet replay. This refers to the recording and retransmission of message packets in the network. Packet replay is a significant threat for programs that require authentication sequences, because an intruder could replay legitimate authentication sequence messages to gain access to a system. Packet replay is frequently undetectable, but can be prevented by using packet time stamping and packet sequence counting.