Last month, I covered two basic Windows NT security topics: creating a day-to-day user account and locking down your workstation when you leave it. But these measures don't make your system impervious to intruders. Determined snoops can easily bypass your log-in security if you use FAT (file allocation table), the ancient DOS file system that still lives on in Windows 9x. If you share your PC, you should also control who can access your files.

Windows NT 4.0 supports two file systems: FAT16 and its own NTFS (it can't read FAT32 partitions). As inefficient as FAT16 is, you may need it if you have to boot multiple operating systems and open the same files from each. To create a partition for each file system, use PowerQuest's $129 PartitionMagic.

Unlike FAT16, NTFS lets you control who gets access to which files. When you installed NT, you had the option of converting the target FAT partition to NTFS. But because the setup program doesn't explain the benefits of converting, you probably didn't. You may be using one file system or a mix of both, which may not suit your needs. To help you choose the optimal system for you, I've listed the pros and cons of each configuration option:

Convert all partitions to NTFS. NT's file system offers the highest level of security and file-storage efficiency among the three options. But it won't let you boot Win 9x or another operating system in order to gain compatibility with software or hardware that NT doesn't support.

Leave all partitions as FAT16. This configuration allows you to boot multiple OSes for maximum compatibility with your older software and hardware. However, FAT16 stores files inefficiently on partitions that are larger than 512MB and the maximum partition size is 2GB.

Leave boot partition as FAT16, create separate NTFS partition. You get dual-booting; files stored in the NTFS partition benefit from higher security, storage efficiency and compression. But dual-booting makes it easier for miscreants to delete your NTFS partition.