The rule 'Suspicious IO.FileStream' is designed to detect potentially malicious activity involving the use of the .NET IO.FileStream class through PowerShell on Windows systems. Specifically, this rule looks for the invocation of ‘New-Object’ alongside ‘IO.FileStream’ and the direct access to a drive volume via the ‘\\.\’ path specifier. This pattern could indicate that an attacker is attempting to circumvent normal file access control and read raw data from the system by obfuscating their intentions in legitimate PowerShell commands. The use of the DOS device path is a common technique in evasion tactics as it allows raw byte access without using standard file APIs, which might be monitored or restricted. To trigger this alert, the Script Block Logging must be enabled to capture and analyze these PowerShell commands effectively. The rule helps security teams identify potentially malicious behavior that could lead to data exfiltration or manipulation through direct file access.