Apple’s macOS surreptitiously creates and caches thumbnails for images and other file types stored on password-protected / encrypted containers (hard drives, partitions), according to Wojciech Reguła and Patrick Wardle, two macOS security experts. The problem is that these cached thumbnails are stored on non-encrypted hard drives, in a known location and can be easily retrieved by malware or forensics tools, revealing some of the content stored on encrypted containers.
ORIGINAL SOURCE: Bleeping Computer