Its discovered that Nigerian fraudsters are able to recover internet banking data stored on recycled PCs sent from the UK to Africa.
The information can be found on a PC's hard disk, which is easy to access if the drive is not wiped before sending.
Anti-fraud expert Owen Roberts said simply deleting files was not enough.
Users should instead use a programme to wipe their hard drive before they sell or give away their PC, a process which over-writes what is already contained on the drive.
Alternatively, people should remove their hard drives before they give away their computers, he said. "It is surprising how easy it is to obtain documents people leave on their computers," said Mr Roberts, who is head of identity fraud at CPP Group.