When a file is deleted from hard drive, it doesn't mean that the file has been wiped from hard drive, the files system just make a "deleted" flag to the data, whihc make us can't see it as normal. Until new data save to the space where the original data save in, it will be overwritten by new data.
Those were learned by me when I accidetanlly deleted some files from my USB drive last month. And the you can use data recovery software to recover deleted files from USB drive. Know more here: http://www.card-data-recovery.com/usb/kingston-usb-data-recovery.html