As the line all but vanishes between work and personal life, it’s easy to forget that the PC you use at work doesn’t belong to you. You give out your work e-mail address to friends and relatives like no one can take it away. You store all your important contacts and accumulated expertise on your hard drive as if they will always be there. You even do your taxes on the laptop you take home. Why buy your own PC when the work computer has so much extra storage space?

But jobless professionals know the cold hard truth: Your corporate PC can be taken from you without warning, a practice that’s common during layoffs. And you may never see your precious data again. “Most companies say, if we own the box, whatever is on that hard drive is ours,” says Catherine Kilbane, a partner and employment lawyer at Baker & Hostetler LLP in Cleveland.

John Francis of San Jose, Calif., learned this lesson the first time he changed jobs, back in 1983. For years, he had been collecting contacts and electronic messages as a computer programmer at Digital Equipment Corp. In those days, all such data was stored centrally on a mainframe computer, and the files could only be read by the system that created them. “It wasn’t viable to take the files [home] with you. The formats were proprietary, and it wasn’t common to have a PC at home,” Francis says. He left with nothing.

Next time, as he was leaving Hewlett-Packard for a startup in 1992, he was prepared. “Well before I knew I was going to leave, I thought about what I wanted to take with me,” he says. He poured all his e-mails and phone numbers into text files, copied them onto floppy disks, and loaded the files onto his home PC.

Even in the early ’90s, copying office files was pretty easy. There wasn’t much e-mail, and the files that common word-processing and spreadsheet programs created took up only a few kilobytes of storage space, small enough to fit on a floppy disk.

Today, transferring computer files is far more complicated. Office workers often have hundreds or even thousands of messages stored on their office e-mail accounts. They rely on old messages to recall names, project details and even contact information. They use many more programs, and those programs can produce a single file too large to fit on a floppy disk.

The good news: Today’s personal backup and storage technology can stockpile large amounts of data, and the prices are reasonable. You can get an external hard drive or backup device known as a Zip drive today for as little as $100, and they work with just about any computer, says technology analyst Rob Enderle at Giga Information Group, a consultancy.

Windows XP, Microsoft’s latest operating system, comes with a utility called Migration Assistant that can keep track of your personal data such as e-mail, Word files and contacts. When you use it to back up, you only need to resave the changes rather than all the files, Enderle says. Migration Assistant also lets you turn all your files into one big, compressed file so that it takes up less disk space.

If you don’t want to buy a storage device, you can use an online backup service, as long as your office PC is connected to the Internet. FusionOne, Connected Corp. and @backup rent Web server space for as little as $15 per month.

You can even program these outside services to back up your data at a scheduled time every day. “So if you get fired all of a sudden, you have everything you had the last time you synched,” Enderle says.

There are even lower-tech ways to salvage your data. One is to periodically print out your most important files, such as your contact list. You can also e-mail important documents as file attachments to a private account, though Enderle warns that some corporate networks prohibit large attachments.

It’s easy to counsel employees never to use PCs for personal business, as experts often do. “My best advice is, don’t do it. That’s the best way to protect yourself,” says Lin Grensing-Pophal, an author of human-resources books including “Telecommuting: Managing Off-Site Staff for Small Business” (Self-Counsel Press). But, she says in the same breath: “Is that realistic? No.”

Her alternative advice is to carefully study the section of the employee manual that talks about PC usage policies. Most companies permit (or at least tolerate) some limited use of the phone, copier, fax machine and computer for personal business. But even lenient companies typically point out that if you use company equipment, you should be aware that the transmissions aren’t private, Grensing-Pophal says.

Should you be escorted out of the building without warning, a last resort could simply be honesty, she says. “Just be upfront and say, I’d like to get some information off my computer,” she says. And if management won’t let you do it yourself, because they’re worried you might steal competitive information or sabotage the system, ask if it could be done with HR supervision, she says. “Most employers will be understanding about that,” she says. “Really, if you’ve been with an employer who’s been a hard-ass, you probably know ahead of time.” Heed those warning signs if you want to hold on to your data. In these uncertain times, they may be your only defense.