Most used cell phones and PDAs contain personal information that their former owners neglected to adequately delete, Trust Digital, a McLean, Va. security firm reported Wednesday.

Trust Digital examined a small sample of used phones and personal data assistants purchased from sellers on the eBay online auction site, and recovered data from 9 out of 10 of the devices.

"The file system on your cell phone or PDA is just like the one on your PC's hard drive," said Norm Laudermilch, the chief technology officer at Trust who restored the data. "If you delete a file, you're not really overwriting the data. All it's doing is changing the index of the file system, or the file's pointers."

That makes salvaging data from discarded devices a snap, said Laudermilch. "It's really very simple. There are free tools on the Internet, as well as commercial tools that can resurrect data. We wrote our own little tool, about 30 lines of code."

Among the information that Laudermilch restored were credit card account numbers, "very sensitive" chat logs, enterprise e-mails about contract negotiations, and computer passwords.

Because phone and PDA data is stored in flash memory, it's retained even if the device's battery is drained or removed. To delete flash memory data, users have to do a "hard reset," which returns the hardware to a factory-fresh condition. Each phone and PDA maker uses a different hard reset procedure; some, in fact, can only be down by a technician or after contacting the phone service's help desk.

Phones and PDAs are not the only electronic gear which aren't properly wiped before they're tossed or sold. Studies of the contents of used hard drives have found similar results: a wealth of data, some of it personal or confidential.

Trust Digital recommended that users secure their cell phones and PDAs using passwords, to lock out casual snooping if the devices are lost.

[Note: This story was updated at 3:05 pm. Statement from Nick Magliato, chief executive of Trust Digital, replaced with quote from Trust Data chief technology officer Norm Laudermilch.]