Does your computer system hold any information that you wouldn't want a competitor to have? Mailing lists? Job quotes? Tax returns? Letters to your lawyer?

What you need is Peter T. Davis' "Complete LAN Security and Control." In it, he helps you identify what parts in a local area network (LAN) need protection and suggests steps to protect them. The writing is clear and mostly free of jargon.Davis starts with an assumption with which we heartily agree: that it's impossible to keep data completely secure on any computer network. Part One of the book explains what a network is and why it's so vulnerable to assault.

Part Two helps you pinpoint where your own network is susceptible to breaches in security. For each vulnerability, Davis suggests easy-to-install solutions. Part Three is full of tips on how to secure your hardware, software and network components.

Part Four prepares you for tomorrow's security problems, such as wireless LANs. The book's appendices contain a useful LAN security checklist and a long list of products you can buy that help with data encryption, access control, security auditing, and disaster recovery.

Chapter 8 details what the various network programs provide for security, from AppleShare to Banyan VINES. A comparative table shows network shoppers what one network can do that others can't. Here, you'll find that Novell NetWare 3 is the only one of five popular networks that includes utilities for server-to-tape backup, disk mirroring and duplexing, and fault tolerance.

(Windcrest/McGraw-Hill, 329 pages, $27.95.)

"Live Wired" is subtitled "A Guide to Networking Macs." Written by computer engineer James K. Anders, it starts with two tables of contents, the usual one and an "exploded" T of C showing subchapter titles! Unlike the previous book, it's heavily illustrated with drawings and diagrams.

Part One explains networking fundamentals in terms anyone can understand. For instance, a walkie-talkie simile shows how networking works. Part Two gets into the nitty gritty of hooking Macintoshes together.

Part Three acknowledges that most office Macs will sooner or later have to be hooked into non-Mac networks. A chapter apiece is spent on MSDOS, Unix, DEC VAX, and IBM mid-range and mainframe systems.

"The key," Anders sums up one of these chapters, "is to first determine the desired services. Then, examine which protocol best delivers that service. Finally, choose a cabling system that balances support for the chosen protocol or protocols with cost and future growth and expansion."

Finally, there are chapters on network design, implementation, management and troubleshooting - and a bound-in disk of some small value in helping you design your network in a word processor. Somehow, the book makes Mac networking seem harder than it is! (Hayden, 427 pages, $29.95.)

Does the idea of installing a wireless LAN or a wireless WAN (wide-area network) intrigue you? "Using Wireless Communications in Business" shows what's entailed. Author Andrew M. Seybold doesn't pull punches. He cites advantages - but also drawbacks and cautions.

"Wireless LAN Guideline Number 1," Seybold says, is: "Determine the physical location." Number 2 is: "A wireless LAN connection should not be implemented unless a payback period that is less than two years can be calculated. It is likely that within the next two years the technology for wireless LANs will have changed dramatically."

Does that make the book useless? Definitely not, says Seybold. "Providing wireless data access today requires a certain level of commitment for success; however, once implemented, users will wonder how they did without it."

The book demystifies data frequencies, cellular digital packets, and various radio systems. It reviews numerous airwaves providers. And it poses some legal issues involved in wireless communication.