|  |  | TCP/IP's source code is available; as a result, many hackers have found security holes in the TCP/IP protocol. Network File System (NFS) and Network Information System (NIS) may allow an attacker root (administrator) access if not configured properly. Operating systems such as MS Windows systems, UNIX, and OS/2 have had their share of security problems. Networking equipment can be threatened by password problems, lack of authentication, routing protocol weaknesses, and holes in Firewalls.