A study of 100 USB drives purchase by Abertay University found over 75,000 files were still intact from supposedly empty drives.
The study, designed to show the importance of fully wiping storage devices when discarding or selling them.
On the drives, there were multiple instances of passwords being stored, as well as banking details.
Strangely, all but 2 of the drives appeared empty at first glance, but the University said that using publicly accessible programmes, it was worryingly easy to retrieve the data.
Although some of the drives had been wiped properly, 42 of the drives had all of their contents recovered, with 26 of them having the files partially recovered.
Prof Karen Renaud, from Abertay University’s division of cybersecurity, urged people to use software designed to fully wipe drives instead of just deleting or formatting it, especially when selling to an unknown buyer.
She said: "An unscrupulous buyer could feasibly use recovered files to access sellers' accounts if the passwords are still valid, or even try the passwords on the person's other accounts given that password re-use is so widespread."