Kristopher Sharrar is regularly asked the best way to completely erase data from a computer.
His answer: steamroller.
"They ask if that's a program," said Sharrar, national leader for Computer Forensic Services at Ernst & Young's Litigation Advisory Service Practices. "I say, `No, that's a piece of heavy construction equipment.'"
Deleted files are rarely truly erased, even when a hard disk is "wiped clean" by some software programs that promise to make computer files unrecoverable, computer security experts say.
Computers can retain files for years. Hitting delete or emptying a "recycle bin" doesn't remove the file completely. Instead, it tells a computer that the space a "deleted" file is taking up can be used again.
Until the space a file is using is reused, the "deleted" document remains on a computer, said Jim Reinert, director of software and services for Kroll OnTrack, a data-recovery company in Minneapolis.
Many hard disks are so large that users rarely have to reuse previously occupied space, Reinert said.
Some programs will run through an entire computer's hard drive and reuse every piece of space, which should wipe a hard drive clean, Reinert said.
Even when that happens, both Sharrar and Reinert say, there is a chance to recover some fragments of a file.