Devices that incorporate sniffing are useful and necessary. However, their very existence implies that a malicious person could use such a device or modify an existing machine to snoop on network traffic. Sniffing programs could be used to gather passwords, read inter-machine e-mail, and examine client-server database records in transit. Besides these high-level data, low-level information might be used to mount an active attack on data in another computer system.

Sniffing data from the network leads to loss of privacy of several kinds of information that should be private. These kinds of information include the following: - Passwords
- Financial information
- Other private data

Sniffing Passwords
Perhaps the most common loss of computer privacy is the loss of passwords. Typical users type a password at least twice a day. Data is often thought of as secure because access to it requires a password.

Sniffing Financial information
Most users are nervous about sending financial information, such as credit card numbers and checking account numbers, over the Internet. The privacy of each user’s credit card numbers is important. Although the Internet is by no means armored, the most likely location for the loss of privacy to occur is at the last points of the transmission. Businesses making electronic transactions giving more careful attention about security as those that make paper transactions, so the highest risk probably comes from the local network in which users are typing passwords.