Not only are they hidden files, but they're also considered protected operating system files. (howtogeek.com)
This is done to prevent novice users from deleting or making changes to critical operating system files that are stored on the other side of this artificial wall. (android.gadgethacks.com)
But you need a good knowledge or experience in terms of operating system files or experience in manual removal of malicious software. (thewindowsclub.com)