o you received a new PC over the holidays, and you're planning to get rid of the old one. But have you carefully inspected all the personal files on the hard drive? Simply deleting them may not make them disappear.

Two M.I.T. graduate students, Simson Garfinkel and Abhi Shelat, found this out in a two-year study. They said they had bought 158 used hard drives at secondhand computer stores and on eBay. Of the 129 drives that worked, they said, 69 still had recoverable files and 49 contained "significant personal information" like medical correspondence, love letters and credit card numbers.

The students reported their findings in an article published last week in the journal IEEE Security & Privacy.

On common operating systems like Microsoft Windows, simply deleting a file, or even emptying the "trash" folder, does not necessarily make the information irretrievable. The information can live on until it is overwritten by new files. Various software products are available for a more thorough hard-drive cleanup.

The Best Offense . . .

Almost every day, it seems, another big employer is announcing job cuts. Although there's no foolproof way to avoid a pink slip, here are a few tips from career experts to help make yourself as indispensable as possible:

• Increase your visibility. Make sure that your boss is aware of your accomplishments, and try to get to know your superiors better. In a downsizing, workers with low profiles are often the first to go.

• Become more productive. If you do your work better and faster, and try to save the company money in the process, you're likely to be noticed. After completing a project, request new assignments or, better yet, suggest them yourself.

• Remain flexible. Be open to new projects and additional responsibilities. By specializing in just one area, you may be more vulnerable in a downsizing. Let your supervisors know that you are willing to travel, or to change cities, if necessary.

• Network. Try to meet people outside your department and keep in touch with old contacts. Most job vacancies, after all, are filled from within a company.