The unauthorized person has all the rights and privileges of the logged in user. Any suspicious activity will be traced back to the user's login, not to the unauthorized person. Windows NT stores the user name and password for all logins on the local hard drive, which the end-user or an unauthorized user may later be able to crack. If an unauthorized user learns the Administrator password, the entire network is open to attack. Be very careful in allowing staff to dial in to their work computer from home.
Any cracker equipped with automatic dialing software can discover the modem.
This can be done with many firewall products. These are some very basic suggestions. The subject of network security is a large one. Many good books are available for those interested in a fuller treatment of the subject. The web version was last updated on April 26, 1999.