Name two software tools used for OS guessing? (Choose two.

Nmap's -O flag performs active OS fingerprinting by sending specially crafted probe packets and matching the target's TCP/IP response characteristics against an extensive built-in signature database to identify the operating system. It is one of the most widely used and accurate OS detection tools available.

Snadboy Revelation is a Windows utility that reveals passwords hidden behind asterisks in dialog boxes and has no OS fingerprinting capability.

Queso is a dedicated OS fingerprinting tool that sends crafted TCP packets to a target and analyzes the responses to determine the operating system based on known TCP/IP stack implementation differences, making it a direct counterpart to Nmap's OS detection capability.

UserInfo is used to enumerate user account details from systems such as via NetBIOS or LDAP queries, not to detect or identify operating systems.

NetBus is a remote access trojan used for unauthorized control of Windows machines and is not an OS fingerprinting or detection tool.