Some antivirus applications may prevent Carbon Copy Cloner from reading certain files, mounting or unmounting disk image files, or, in general, degrade the performance of your backup. In some cases, antivirus applications can even affect the modification date of files that CCC has copied, which will cause CCC to recopy those files every time as if they have substantively changed. In another case, we have seen such software create massive cache files on the startup disk during a backup, so much so that the startup disk became full.