And we can usually keep the intruders out, but only if everyone knows about the threat and takes the right precautions. Intruders use a variety of techniques to gain unauthorized access. A password cracker will use a program that automatically keeps trying to log in to the system by using a series of easily guessed passwords, or using a dictionary as a source of guesses. That approach can be defeated if users follow the guidelines for password selection and security. NIH system engineers keep alert for those types of threats, and try to stay one step ahead of the intruders by fixing the errors and closing the trap doors.
Network spoofing is an ingenious way for an intruder to gain access.
The intruder sets up a program that impersonates the sign-on routine for another system. When you attempt to log in to the system, the intruder's program collects your password, then returns a message that the system is unavailable. An intruder's program can collect hundreds of valid passwords using this method. NIH system engineers keep on the lookout for these types of tricks, but all users need to change their password on a regular basis to defeat this type of intrusion. All of these types of break-ins are illegal.