An employee reports that someone has logged into their system and made unapproved changes, files are out of order, and several documents have been placed in the recycle bin. The security specialist reviewed the system logs, found nothing suspicious, and was not able to determine what occurred. The software is up to date; there are no alerts from antivirus and no failed login attempts. What is causing the lack of data visibility needed to detect the attack?

A.	The threat actor used a dictionary-based password attack to obtain credentials.
B.	The threat actor gained access to the system by known credentials.
C.	The threat actor used the teardrop technique to confuse and crash login services.
D.	The threat actor used an unknown vulnerability of the operating system that went undetected.