As we've all learned from recent events, simply hitting the delete key doesn't mean the computer file in question is really gone. While the information on your office's hard drives probably isn't sensitive enough to bring about an impeachment, a file-shredding program can ensure that a decommissioned computer doesn't still contain last year's operating budget.

File-shredding software corrects a glitch in the way your computer erases files. In most cases, the actions you take to delete a file only remove the file name; this signals the computer that the space occupied by the file is available for reuse. The contents of the file remain on the hard disk (and are often recoverable by most file recovery software programs) until the space is needed and over-written with new data. On large hard drives, it can be months before deleted files are truly erased.

Shredder programs, sometimes called auto-scribblers, immediately overwrite deleted files with random characters, making it virtually impossible to recover the information. Different versions of the software mainly differ in how many times they overwrite the deleted files, and how efficient they are in tracking down hidden copies like swap, backup and .tmp files.

Even low-end file-shredding programs, which start at around $30, are trustworthy as far as erasing the file for good. As long as the data is overwritten at least once, and the program also finds and overwrites the version in the memory swap file, you're safe from your average set of prying eyes. Higher-priced versions, which range up to $99, include further levels of protection for the paranoid, with some featuring the ability to overwrite data up to 12 times. Although impressive, it may be more than you need -- it's generally agreed that twice is sufficient to foil everyday attempts at recovery.

The extra money you pay for a higher-end program will get you better reporting. For those who sleep better with concrete proof that all traces of a file are gone, more expensive programs will generate a verification list of what's been shredded. Low-end programs often simply give on-screen confirmation.

Another big difference between shredder programs is whether they run in the background or are started manually. On the high-end, there are programs that automatically overwrite any file sent to the recycle bin. Several cheaper programs require the user to select and drag files to be deleted to destroyed. If most of your files are not that sensitive, this type of program is considerably more forgiving since not all files are wiped away automatically.

A capability touted by some file-shredding programs is that their "search and destroy" activities extend to Internet browser records. Memory caches containing the web pages you've visited and pesky cookies are sniffed out and eradicated. Although it may seem impressive, to be honest, it's pretty easy to do yourself. Similarly, it's important to remember that several vendors also sell the same software to the U.S. government. This means that some of the bells and whistles, such as meeting Department of Defense security standards and special one-key "panic" delete functions, while sexy, aren't really worth the extra money for most offices.

Quick tips

Not everything can be destroyed. Some file-shredders can't see files deleted from MS-DOS; in other cases, database files are immune. Ask about your particular type of files before buying. Not everything can be recovered. Although a file recovery utility can be used to restore accidentally deleted files, it can be a time-consuming task that can not always recover what you want. Back up regularly instead. Selling your computers? Erase them first. Although a vendor may promise to erase your hard drives, it may not happen. Taking the time to scrub hard drives thoroughly is an important step to take. Beware of add-on encryption. Some low-cost file-shredding programs are sold bundled with encryption programs. Cheap encryption is rarely a bargain-don't expect much from it.