If you're working with a lower version than the latest one, you may hit a similar message: This CKEditor 4.22.1 version is not secure. Consider upgrading to the latest one, 4.24.0-its.

To solve this problem, add the following configuration line:

CKEDITOR.replace('your-textarea-id', {
    versionCheck: false
});

PERSONALLY, I didn't upgrade any tool unless there was a critical security issue so, if the version you use has a security issue, you should quickly consider upgrading it.