Q When exploring the external drive that I use with my new Mac mini, I discovered a load of files with bizarre names like cp.properties, cpbf0000000000000288581, and the like. Altogether these take up more than 30 GB so I am keen to trash them. But when I try to remove them, they only reappear. Are they used by OS X?

A No: those files are backups created by CrashPlan. The only way that you will be able to remove them and keep them away is to disable or uninstall CrashPlan.

Before doing so you should consider carefully whether you wish to use the belt of Time Machine, the braces of CrashPlan, or both belt and braces.

Updated from the original, which was first published in MacUser volume 29 issue 7, 2013.