With Windows 2000, without a valid user name and password no one gets in. The nice thing about it is that there can be accounts for each member of the family. As administrator, you can set up accounts for each and specify different access rights for each. Personal data files can go into a folder with restricted access, perhaps to yourself and your spouse. Other options include blocking certain users from installing programs, or even running certain programs.
Security also protects from outside attacks.
Under Windows 2000, it's a lot harder for malicious programs to wreak havoc. Cable modem users who find that with constant access to the Net their computers are more at risk, can use the added security of Windows 2000 to help reduce this risk. Windows 2000 is the latest version of Windows NT, which means it is a full 32-bit operating system. But previous versions of Windows NT were known to be very difficult to install and configure, definitely not for the typical home computer user. Getting a system up and running almost required a computer science degree.