To solve this question, the user needs to understand the concept of file security and how confidential data can be exposed.

Option A is incorrect because using special characters in the filename does not necessarily keep the file hidden or secure. The filename is just a label for the file and does not affect the file's contents or accessibility.

Option B is incorrect because the amount of time the file exists does not determine the file's security. Even temporary files can contain confidential data, and it is essential to ensure that they are adequately secured.

Option D is also incorrect because using special characters in the filename does not necessarily indicate that the file is a system file or secure. The filename is just a label and does not affect the file's contents or accessibility.

Option C is correct because file permissions play a crucial role in determining who can access or modify a file. If the permissions are not set appropriately, anyone can access the file, including unauthorized users, resulting in confidential data exposure.

Therefore, the answer is: C.