Is it ever right to spy on how someone uses a computer? Your answer might depend on who you are. A frightened parent in this summer of abductions might feel differently about monitoring chat room sessions than, say, an employee whose corporate bosses were watching him.

And with terrorism in the air, not to mention corporate espionage, crooked business deals and child pornography, spy software will always have its defenders. When and where to deploy it is an ethical question that end users now face, for these programs are widely available.

The most comprehensive one is Investigator 4, from Kennewick, Wa.-based WinWhatWhere, a program so effective it puts chills up my spine. Investigator will track every keystroke: letters, backspaces and returns.

The program produces two logs, one with key-by-key text, and one that strips the extraneous stuff away to make the text understandable. Nothing is sacred. If someone put Investigator on your computer and you went online to buy something with a credit card, Investigator would record the transaction, including the credit-card numbers.

Do you sign onto a secure site using a password? Investigator can read the password, and its logs show the date and time of every access of the site. Reading a message from a secret admirer? The software logs any kind of e-mail: messages in Outlook, Web-based programs such as Hotmail. And forget about deleting words. Everything you type is on those records: every mistake, every addition.

And keystrokes are just the beginning. Investigator can use a Webcam to take covert pictures of whoever is using the computer. Anyone attempting to use the machine when its owner is away from the desk is clandestinely photographed.

If you think you'd know you were being watched, guess again. Investigator can hide itself completely, moving and renaming its critical files at random to make it difficult to find. It performs all functions -- including e-mailing reports on what it discovers to the person who installed it -- without visible effect. It operates without a system tray icon and isn't found by anti-virus programs.

Fortunately, you can't catch Investigator over the Internet like a virus. It's a full-blown program, one that must be loaded from its CD-ROM directly onto your PC. But if someone loads it, the program can follow you to a Web site and take screen shots of what you see. It can record both sides of a chat-room session with ease.

I've put off writing about this category of software for years because of the ethical issues it raises. But the $100 Investigator is now widely reviewed, and in use by law enforcement agencies, private detectives and individuals. I can't answer its moral conundrums, especially when it pops up in sleazy divorce cases, but I thought you should know about it because computer monitoring is widespread.

Some companies use Investigator to track employees, checking for time-wasting activities or identifying cases of sexual harassment. In fact, the American Management Association says 63 percent of large and mid-sized companies monitor Internet use in one way or another.

In my view, companies that do monitor should make it clear to their employees that they're being watched. And employees need straightforward guidelines about the company's computer use policies.

Companies argue that they don't want to waste computer time on people with Internet addictions, and protecting themselves from lawsuits is essential. I can appreciate such concerns without losing the conviction that monitoring should be obvious. Investigator 4 can be set to run in visible mode, which is precisely where I would leave it.