Frequency and risks of changes to clones

Code Clones - duplicated source fragments - are said to increase maintenance effort and to facilitate problems caused by inconsistent changes to identical parts. While this is certainly true for some clones and certainly not true for others, it is unclear how many clones are real threats to the system´s quality and need to be taken care of. Our analysis of clone evolution in mature software projects shows that most clones are rarely changed and the number of unintentional inconsistent changes to clones is small. We thus have to carefully select the clones to be managed to avoid unnecessary effort managing clones with no risk potential.