|  |  | Some software programs have been problematic since their creation. NFS, NIS, and sendmail have had security vulnerabilities published since they were released. NFS uses an IP address for authentication, and any IP address can be spoofed. Sendmail applications are known to be troublesome, but can be searched to reveal possible attacks. Windows 95 may allow users to login without passwords. Windows NT may have a guest account with no password. All systems running UNIX and NT should have all of the latest patches and service packs loaded to ensure that these security holes have been filled.