This allows the scanners to determine what services are being used, what users own those services, whether anonymous logins are supported, and whether authentication is required for some network services. A password cracker is any program that circumvents password security by revealing passwords that have previously been encrypted. Since passwords are encrypted with robust algorithms, it is nearly impossible to decrypt such sensitive information. What is done instead, is to simulate the same algorithm used to encrypt the original password through comparative analysis. A trojan horse is an unauthorized code contained within a legitimate program whose functions are unknown to the user, a legitimate program that has been altered by the placement of unauthorized code within the program covertly , or any program that appears to perform a desirable and necessary function but actually does something additional that is unknown to the user.
Sniffers are devices that capture network packets.
Their legitimate purpose is to analyze network traffic and identify potential areas of concern.